There are reasons to get a PC besides exclusives.
1.)
Free mods and updates: Your games gain exponentially greater replayability with mods. If you buy a popular game like Half-Life 2, it's as if you are buying 100 games because there are so many unique mods out there. Also, DLC you might be paying for on a 360 or PS3 is usually free on a PC. For example, the recently Left4Dead "Crash Course" update added a new campaign to the game. PC users didn't have to pay a dime for this.
2.)
"Backwards Compatibility": This is sort of a funny concept for PC gamers, because they've always had it to a certain degree. Some older games don't run well on newer operating systems, but there are usually ways to find workarounds to get past that. The PC library stretches back for decades. No console can say that.
3.)
Emulators: With a single computer you can play just about every old arcade or console game ever created... if you don't mind bending the law a little bit.
4.)
Online is easy: The internet is not something new for computer users, so it's usually not such a hassle to play online. And nobody is dumb enough to try to charge you extra for that like Xbox Live does.
5.)
Digital Distribution Deals: Yeah, you don't get a box and your manual is a .pdf file, but companies are getting better about making it worth your while. Plus, the prices can get remarkably low, in case you haven't noticed some of my ongoing threads:
http://racketboy.com/forum/viewtopic.php?f=26&t=13915
http://racketboy.com/forum/viewtopic.php?f=26&t=16494
Plus, you can be my friend on Steam.
