The iMac is an AIO. The upgrade potential of an iMac is no worse than any other AIO PC.
If you are comparing an AIO to a full tower, 110% fully upgrade capable piece-built PC, you're really grasping at straws comparisons wise. Ford vs. Chevy arguments are silly.
Two completely different beasts. By that logic, the iPad or iPhone, or any other device that cannot be upgraded by the user is a POS. Yet people still buy them by the millions every single quarter, and market share is growing year over year for all these overpriced products.
AIO's aren't for me, nor you apparently. That doesn't make them useless to the world as a whole. We could sit here for eternity and debate whether or not Apple products are overpriced as a whole, and I suspect our opinions would end up on the same page in the end
That doesn't change the fact that the iMac, the new one or one from 10 years ago - suits a lot of peoples needs just fine, and people buy them in spades. Some people simply have no need to expand their machines past what the factory offers. I do, some don't, and that's just fine by me. It also doesn't change the fact that in 2013, Apple sold 16 million Mac's, and I suspect a vast, vast majority were iMac's. Someone obviously finds them to suit their needs. I don't happen to be one of them, 5k gorgeous display or not.
The new 5k iMac is actually only $500 more than last rev non 5k machine, and if you can point me at a comparable 27 inch 5k monitor AVAILABLE NOW for $500 I'll eat my hat. Hell, I'll eat your hat, too.