That is a nice achievement. I'm pretty surprised that Mw3 or BF3 didn't have that one in the bag.
COD churns out every year. Console gamers are fine with that(just look at those sports series) but I doubt many PC gamers will buy it every year.
As for BF3, you can't even buy it on Steam. You can only buy it on Origin.
But still, Skyrim is selling pretty well. I hope Bethesda will put more effort into the PC version in the expansions or the sequels. Obviously PC gamers are far more than the 10% Todd claimed. And each PC copy sold brings far more profit than a console copy(PC don't need to pay royalties to Microsoft or Sony. And publishers can get back around 70% for digital sale while only 30% or less for retail copies.)