I think a big part of the problem, as Rhezuss points out, is that console games make huge money, and PC games don't. And this has been a trend for a while, and PC games have been on the decline. And it's a snowballing process, because as more people jump ship to consoles, a good percentage of the people that are still on the PC platform are pirating their games anyway.
I was talking on gChat with a friend yesterday morning, telling him how I finally broke down and bought MW3 on release day, the first $60 game I've bought in years. He was like, "I didn't realize that was out! Grabbing the torrent now." Followed by the expected, "If I like it, I'll buy it." Dude hasn't bought a game in years.
There aren't good PC exclusives anymore because most PC gamers are dirtbags, and most of the people willing to actually pay for good content have migrated to consoles.