If a good chunk of people use one OS, then game developers will happily develop for it.
Unfortunately, Linux is only 0.8% of the desktop market and most of those people are either willing to duel boot or have a console or go without games.
That 0.8% is split between different distros (Ubuntu, Redhat, Gentoo), which are rarely binary compatible. Then there are different versions of each distro (Fiesty/Gutsy). Thats before you start thinking about KDE and Gnome.
If you wrote a game in 2001 for xp, you could get away without patching it for 6 years.
If you wrote game for Linux in 2001 there is little chance you play it now without recompiling it for your kernel, which you would not be allowed to do because it would no doubt be closed source.
While some closed source developers will keep up with the development of Linux for most popular distros, this is an advantage for them because they can sell new versions. Games are different once a game is released and sold, there is little benefit to the writers in keeping it compatible.
Until there are sufficient users of one distro games on Linux will stay hit and miss.