Personally, I enjoy PC gaming for quite a few reasons:
High customizibility with, for the most part, ease of doing such (Xbox owners have to jump through some crazy hoops to get their Alyxs naked)
The loads and loads of indie games that will probably never end up on Xbox Live Arcade (and I'm not talking about the big popular corporate-backed indie games)
Mods (Garry's Mod, Research & Development, Trespasser, Pirates Vikings & Knights, that one that turns Civ IV into an alien-fighting real-time RPG, all that good stuff)
And Warp, the emphasis in my post was on "missing out on". As someone with such a sophisticated taste in games, I don't consider the Beatles, an assload of shmups, and Mega Man 9 to be reason enough to buy an Xbox. I do consider Dead Rising, Halo, and GTA IV to be, though, and along with lots of others.