I'm only buying a desktop because I want better performance but needed a laptop and wanted to be able to play games in the mean time. I could have just as easily went with a cheap $200 netbook and then the $600 desktop, but that wasn't what I wanted. That adds up to $800, which is twice what a PS4 costs, but how many are spending close to $400 for a general use PC in the first place? It's a higher up front cost, but it balances itself out.
Then you are also getting: A) significantly better performance, B) a far larger library of games, C) cheaper prices on games, D) access to tons of mods and ways to tweet your games, E) free online, and a myriad of other advantages.
I know I'm just sounding like a PC elitist, which isn't my intention, but people are still looking at it from the wrong angle and using that as an excuse for why the like consoles better. There are reasons for liking consoles over PC, but I wouldn't consider cost one of them.
EDIT: and I forgot to add that in this scenario you're getting two PCs. Cut out the netbook and it's $600, which is only $200 more than a PS4 and you will wind up saving far more over time.