Why wouldn't you accept this for yourself?
We're pretty off-topic, at any rate to be crystal clear, I specifically commented on the statement "Latest tests with NF-S12A, after 30 minutes prime95, completely stock i7 3770; core temperatures barely reach 70°C". With reference only to that statement, I don't rely just onto Prime95 and 30mins or a few hours of stress-testing, and this is about the half of what I'd not accept for myself.
As a matter of fact, before validating any system of mine, I'm used to test it for stability and overheating using at least Prime95 and FurMark for 24hours continuatively, to which recently I've added a concurrent session of the Anvil's Storage Utilities Endurance Testing, using the logging feature of SpeedFan to log selected temperatures (CPU, GPU but also any motherboard/chipset sensor) data all over that test. Sometime I repeat this procedure logging the fans rotational speeds instead of temperatures.
What's tricky in validating a fanless system? IMO/IME the overall noise signature and the system heat build-up, mostly: and as ggumdol noted, I don't feel comfortable with any CPU temperature which looks like (IMVHO) too much near to the CPU Tcase max, especially a continuously one: and this is about the other half of what I'd not accept for myself.
I am perfectly aware that all and each of the those halves are heavily questionable: nonetheless that's just a concise and frank answer to your question ("Why wouldn't you accept this for yourself?").
Eventually I'd like to stop my off-topic answer with the same closing stating of my previous post: if you're happy with your results, who am I to contraddict them? Cheers.