The things to look for in a case:
1. Good intake. You can't cool the stuff inside if you can't get air in. Look for open, unrestricted bezels. The Sonata is "ok" in this regard, the Chenbro is better. I think the Fong-Kia 330 os about the best I've seen. (there's a review of it in the cases section on the front page)
2. Good exhaust. The counterpoint to intake. 120mm fans are very popular lately, and all three of the above mentioned cases have them for exhaust, but a pair of 80mm fan mounts works well also.
3. "Sturdiness". Not exactly the right word for it, but close enough. What you want is a case who's side panels won't vibrate when the stuff inside the case vibrates. (Resonance is the technical word for it) That's the problem with most aluminum cases. Aluminum is used to make cases lighter, and for that reason their side panels are usually very thin, which makes them more prone to resonating. Steel cases have stronger, thicker, and heavier sides (generally) which makes resonance less likely. Adding the sound foam to the Lian-Li does the same thing, only more expensively. (Why pay extra to make an aluminum case not resonate when I steel one won't for free?)
So, to answer your question: No, there's no need to buy a case that's specifically sold as "quiet", so long as you look for the important features. Some "quiet" cases, like the sonata, include other minor features that help in the quieting, like rubber bushing for the HDD's, but their effect can be easily duplicated in a non-"quiet" case.
Hope that helps. If anything it opens up your case choices. Which I suppose is either a good or bad thing, depending on how much more time you wanted to spend shopping for cases.