Actually it has more to do with development cost.
Say you're a developer. You find a problem with one type of video card is reported.
Creates a console bug.
Now all consoles can't play because of the bug fix.
So you recode...
test now all users of nVidia cards are SOL.
Of course it might be something like an exploit is found where a console user is able to instakill PC users... Or a PC user is able to instakill console users. A fix would disable some feature that made the game playable for the other side...
Then add on the larger DLC that PC users would like. I mean would console users be willing to wait for more than a gig of data to be transferred to their system? How about 3-4 gigs. I mean I can leave my PC running for days at a time... How many console users would leave their 360 running for 8-10 hours without playing another game(forgive me if you can get DLC while playing other games... I haven't checked). I can on a PC start the download, then chill out reading Lucasforums, listening to the latest Lucascast, or juat leave the download running as I go to sleep. Every two or three weeks, another smaller download, and every two months a big update... Would console users put up with it?
"I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it." Thomas Jefferson