The games
Buy a Wii and a 360 if you want, try playing MGS4, Gran Turismo 5, or Final Fantasy 13 on either of them and you might realize why the price of the PS3 is worth it.
Games make the system, the system doesn't make the games. And if that means that you need to spend a little more on a system that has the games you want then why not do it? I honestly still see nothing on the 360 that I want, and it's been out for awhile now. I could buy it and get "next gen graphics" but I'd be stuck with games that I don't really want to play. Don't fall for that trap, unless you like the games coming out for a system do not buy it.