And how long have you been buying Apple products? Except for the Power Mac/Mac Pro, I recommend you examine the past 10 years of Apple consumer desktop design and tell me if you notice any patterns.
I've been an Apple owner for a decade and a user for nearly thirteen years. I'm aware of the patterns existing in their desktop design. This is why around a year ago, I swore that the only Apple desktop I'd ever buy or use would be a Hackintosh. This is also why I own one Mac and it is a MacBook Pro. This is also why when given the choice between an Ivy-Bridge GeForce-GT-650M laden 15-inch MacBook Pro with a retina display or one without, I opted for the one without and haven't felt even an ounce of buyer's remorse. I recognize that the Mac I bought will most likely not be renewed in the Haswell refresh where the one I didn't will, and that's fine. In 6 years when I'm ready to replace my MacBook Pro with a new model, I will be ready to give up the features that made my current one so appealing. In a laptop, compromises are far easier to stomach than they are in a desktop.
This is not an argument about operating systems, but physical hardware. Obviously the vast majority of my 200+ title library are not available for OSX, which is why I bootcamp into Windows.
The argument here is gaming between Mac and PC hardware, and your assumption that I and many others would not be a frequent gamer just because my hardware happens to only be a Mac, is false.
Then I make another assumption that is most likely true: you don't care about hardware or upgradability.
If you did, you'd quickly realize that an iMac is a terrible deal and that for the price of a 27" iMac that is respectable for gaming (both in Windows and in OS X) you could buy an entry level non-retina 15" MacBook Pro and have enough left over to build a PC tower that is just as powerful as said 27" iMac would've been. Trust me, I once loved the design of the iMac and was completely determined to eventually buy a 27" iMac, but for a variety of reasons, it's the least practical Mac that Apple makes, and I don't have the money to spend on a computer that isn't practical. The best thing someone buying a new 27" iMac can do if they want to use it for gaming like you do is to splurge on the storage, processor, and graphics now because upgrading that stuff later is tricky let alone nigh-on impossible. Again, if you have the money to do that, congrats. Most people don't. I don't. If I did, I'd probably sell my tower for an i7 27" iMac with a 3TB Fusion Drive and the GTX 680MX (as that'd surely best my tower equipped with a Phenom II x4 and a Radeon HD 6850) and when I wanted more oomph, I'd throw out that iMac and get another one.
The iMac has never been user-accessible as far as I know. And if I'm not mistaken, the recent iFix it tear down shows that hard drive in the 2012 iMac is just as difficult to replace as it's past iterations.
So not sure why your griping heavily on the thinner design of the 2012 iMac if servicing conditions aren't much different than from the past.
I never said they weren't bad then either. Frankly, they could make the machine non-accessible and still have it be reliable. The 2009-2011 iMacs were neither accessible nor reliable. In the case of the new 21.5" iMac, it seems as though all of the problems that would contribute to poor reliability have been resolved, albeit, at the cost of using laptop components in places where desktop components were previously used.
For a desktop at that price point, much like the Mac mini, this makes for a poor expenditure of money; paying a premium for slower hardware. But in the $600-1700 range and for those that want a Mac desktop, but won't use it for anything crazy intense (like serious video editing, rendering or gaming), the only options are Mac mini or 21.5" iMac. And frankly, for the various clients that I consult with, I'm glad that the 21.5" iMac is now a reliable option.
For those that will never need to access their hardware, the fact that these machines are not user-accessible is not a problem. But for me, I want to maximize the life of the machine. If my hard drive dies outside of AppleCare, I don't want to be stuck having no choice but to go with an Apple OEM drive. That's costly! Luckily, on the Mac I do own, if my hard drive dies outside of AppleCare, I can buy my own replacement drive and likely have it be a larger drive than what I originally started out with.