It's not.
Yeah, that's really all I have to say to that. I am playing TF2 in the ever expanding competitive playerbase (which isn't shrinking, without a doubt, in fact ESEA seems to have more and more teams every year register)
And to top that off, I recently added Starcraft 2 to my game library, which I feel has a good 6-10 years in it, if it lasts as well as Starcraft 1.
I think idiots came under the impression PC gaming was dying because the lack of Q4 titles that hit the PC. Black Ops wasn't a PC exclusive, but we're about to get into the good stuff, with Portal 2 just around the corner, Bioshock Expansions, and Bad Company Vietnam (btw, Bad Company 2 for PC is still going strong with no end in sight...too bad the games nearing it's death as we speak as far as consoles.)
And on that last note, PC games are played a lot LONGER than Xbox/PS3 games. No one really hears about PC games because PC games last forever...lots of people still play Modern Warfare 1, and it's as good as dead in console land...