So yes, it's mostly for people who want a fanless PSU, without any serious reason.
For example look at allwinner's setup - 9.2cm fan on video card, 9.2cm fan on CPU heatsink, 8cm outtake fan. This is exactly the setup where this PSU doesn't make any sense to use. Those fans will generate a lot more noise than the PSU fan in Seasonic X models with fan up to 400W. And now considering that setup will probably use up to 300W max, the PSU fan will kick in only when you will go over the load where your video card and CPU fan heatsink are already at noisy level.
If he would have a fanless video card, a Scythe Ninja 2 running passive and one 12-14cm fan running at very low speed, i say ok - that is a real use for this PSU. But then you get back to the basic problem, and that in this way you are able to cool only loads where X-650 is running passive too. The difference between X-400 and X-650 is in 200-400W range, and this is the range where i just can't imagine the load which would make PSU fan noise irrelevant.
After analysis of the options, I don't think the issue is as clear cut as you suggest.
My htpc uses an nForce 750 chipset, an Athlon x2 3800 65w, an Nvidia 8800gt video card, and an OCZ 60gb Vertex SSD. The PSU is a Seasonic S12-500 500w PSU. At the time of purchase (2006), it was highly regarded both for its build quality as well as its quietness. It's still highly respected and you'll still see posts referring to this PSU but it's hard to compare how loud it is to current PSU's b/c the testing methodology may have changed (perhaps Mike can comment). Here is the SPCR review of the unit
It is hard to discern which of the fans is the loudest. The 3 fans are all low-rotation fans that are controlled to spin near their lowest rpm. You have to be within 2-3 feet with no ambient noise to hear anything (I sit about 15 ft. from it). However, it appears the audible noise radiating from the case is not fan noise but rather very mild vibrational noise that seems to eminate from the PSU.
In a low-rpm fan environment reducing the number of fans most always assists in reducing noise/vibration. Thus, I disagree that this is the type of setup where a fanless PSU doesn't make any sense to use. Does it add a significant benefit that justifies the cost? That depends on the purchaser and the particular factors.
Would flipping the PSU such that the intake fan is facing inside the case essentially eliminate the noise from the PSU fan? Perhaps, but not if the noise is actually slight vibrational noise. OTOH, depending on the sensitivity of the fan controller, it could result in increasing the fan speed due to increased temps (unlikely given the airflow in the case but....).
Would a newer PSU with a fan that is quieter be functionally equivalent given that I do have 3 fans (no matter how quiet)? Perhaps. But that again raises questions of value. Let's look at the options.
In terms of cost savings, I could go with the Nexus Value 430 (listed as the 2nd quietest PSU in the review). In fact, this is about the only option that provides significant cost benefits. I would spend $89 (not cheap by any means), lose modular cabling, have a less efficient PSU, a warranty of 2 years (vs. 5 on the Seasonic) and still have to deal with the uncertainties of a fan, which include, among others: (1) Over time, fans typically get louder; (2) Fans are not too infrequently defective and get loud quickly; (3) Inconsistency - my experience with PSU fan noise levels even among well-recognized brands is that they're inconsistent at best. All of these create risks that I have to pay to return the item and deal with additional headaches of reinstalling, etc. I'd rather spend the $135, gain 3 years of warranty and not have the headache of dealing with fan related issues. Of course, having a fanless PSU removes the difficulty of trying to optimize fan levels b/c you have one less fan which may or may not be giving off noise or contributing to vibration.
Other options, gleened from page 6 of the review listing PSU's with the lowest sound signature, are even less attractive.
(1) ENERMAX MODU82+ 625w PSU. Alas, it's less efficient at the draw the htpc is running, has a 3 year warranty and is the same price as the fanelss. Plenty of reports of loud fans. Guess that's out of the equation. What may, or may not, be the 500w non-modular equivalent currenctly goes for $100 ($80 after MIR at the moment). Alas, not modular, 3 year warranty but it does come with the ever fun and exciting game of "fan roulette." No thanks. Enermax Modu 82+ 425W? About $120 shipped if you can find it - not as quiet as the Nexus Value but it is modular.
(2) Seasonic M12D 850W. Even more expensive and less efficient at low draw.
(3) Antec CP-850. At $105, it's cheapar but still has a fan that's always on and is less efficient at the loads operated. This PSU is not a standard design and can only be used with certain cases (iirc, 3, maybe 4, cases). This rules out the majority (including htpc use).
(4) Coolermaster M700W. $110-15 shipped....not much savings and certainly not silent. Besides, I went through 3 Cooler Master "silent" or "quiet" PSU's in search of "quiet" to no avail (admittedly I haven't used the line in question but Coolermaster lost me as a customer with what was obviously deceptive marketing with the units I had).
(5) Nexus RX-6300. Untested but comes recommended on the forums. Alas, $130 & still has a fan.
Given the value comparison of these other units, I disagree with you that this fanless unit does not bring a competitive value to this niche market. In fact, only the Nexus Value can compete and it does so poorly above 200watts (arguably not my htpc during standard operations).
This evaluation merely emphasises the primary question to be answered that we've seen over and over (in this short time period of these products existence): To buy the x-400, x-650 or the x-750. After all, the 650 is actually cheaper at the moment, provides headroom for higher demanding rigs and is essentially fanless for low power draw usage (such as an htpc or when using the PC for day to day tasks). I haven't come to a firm opinion. There are a lot of factors to consider (ie., future proofing, swapping opportunities, resale, efficiency disparity, etc.). I'd like to see a version with a fan that remains off until 350-400w and is spec'd to 800-850. Ultimately, neither the 650 or 750 provide safe headroom for absolute silence except in conservative usage. According to the SPCR 650 review (p.3, bottom chart), the "hybrid silent fan control" keeps the fan off up to 20% +-5. The range of power draw to maintain silence for the x-650 is 97.5 to 162.50 (with spec at 130w), while it is 112.5 to 187.50 (spec at 150) for the x-750. Any gaming or encoding load on a mid-range PC/htpc may bring the fan to life (althogh they're clearly very quiet at low draws). Thus, these aren't a real substitute for the x-400 (and that doesn't take into account the greater cost of the x-750).
It'll be interesting to see what the fanless 460w offers. Given the close power rating to the 400, it seems to be unnecessary. Offer 1 or the other but if a PC is really pushing for that extra 60w, then it probably needs a different PSU altogehter. Or, convert that 460w to a hybrid fan control 350/750w and we'll all be happy.
Note: The 80mm rear fan in the diagram is in the wrong position - it's actually on the rear-inner spot while the rear-outer spot fan is off). Fanless might be possible on this htpc but would probably be pushing it, particularly when gaming (which I don't do frequently on the htpc but will every rare once in awhile).
Ultimately, before purchasing this unit, I would disconnect all of the fans to better ascertain just how much noise the PSU is really giving off. I did that in the past to optimze the # of fans as well as fan speed but I don't recall the results vis a vis the PSU.