I used to be a big PC gamer during the PS2 days. I still loved my PS2 and all the good games, but PC gaming was so much more advanced at the time. Comparing a PS2 game with Half Life 2 was a big difference. I had a beast PC. I upgraded my 4600ti to a $400 6800GT. I was blowing money into PC gaming like crazy all to max out games like Doom 3 or Half Life 2. I enjoyed it, but 3 years later i saw the truth.
In 2006 i bought a 360 and pretty much gave up on PC gaming. Games like Gears of War that year looked better than the stuff i was playing on PC. The following year i see the 6800GT i bought in 2004 is completely outdated and cant even play Crysis at low. That year i also buy a PS3... bad start with no good games, but once they start coming... wow!
Recently i bought a very good laptop. I learned from past mistakes and did not waste loads of money on a power hungry desktop beast. My laptop is good, i5, 6GB, 630m. Multiplat games like Dead Space, Fallout, Mass Effect, all look a bit better running maxed out on my laptop than on the 6 year old PS3, but if you compare exclusives PS3 wins. I got STALKER running maxed out and i compare it to Killzone 2/3... sure STALKER is semi open world, but man does Killzone look better. And sure a power hungry beast desktop that can play Witcher 2 on ultra and Crysis on ultra and full of graphics mods beats PS3, but these people are a minority... a minority i used to be part of and dont want to be again.
PS4 is about a year away. I would be pretty dumb if i waste $1000-$2000 on a desktop knowing how outdated it will be. Paying $500 for a 680GTX and knowing it will struggle with new games 3 years from now. If you are rich and have that much money to burn on games... well go for it. I rather pay $350-450 for PS4 and know i can play games for years while the 680GTX will be about as useless as my old 6800GT.
Graphics gap this gen wasn´t as big as last between PC/console and it will be even smaller next gen. Also, with the optimizing the guys at Naughty Dog, Guerrilla Games, and other Sony devs will do on PS4... and the budget they have... i actually think PS4 will be graphics king for a good while.