I've given it a bit of thought, given the recent complaints of several games that don't seem to make any real effort to not be a port (I'm looking at you borderlands and Call of Duty 6). If you think about it, Developing for the PC is not a great decision for Developers for several reasons, which i've thought of here (feel free to add)

1. PC gamers demand Quality. Developing for the PC over a console is much harder and more expensive for several reasons: PC gamers expect the graphic quality to be much higher than any console gamer would, Also, PC gamers demand much more depth in gameplay, especially in terms of controls, of which they can spend time completing and talking about. Console games have much fewer capablities in terms of controls, therefore limiting gameplay depth somewhat, and Console gamers generally don't want in depth gameplay, just quick action for a bit of a fix.

2. PC gamers Complain. No matter what happens, It's guaranteed someone will complain about some aspect of a game that they don't like, whereas others will advocate, and they expect developers to listen to them. This means petitions, Emails, etc, And most companies ignore these and are just another headache.

3. Console Gamers Don't demand Constant Updates. Sort of links in with the previous one. PC gamers want gameplay fixes, glitches removed, and other general fixes throughout the life of the game. Console Gamers rarely bother with this, and are fine with the occasional update.

4. After all that, PC games Sell for At least $20 less Almost universally in Australia, Giving them even less incentive to put effort into a port that less people will play and they'll pay less for.

To me, This seems selfish and all these points are from a marketing point of view, but then again, everything seems to be these days.