Nope. Its called "Market Share". Nevermind theres so many linux distributions at this point, it would be near impossible to ensure universal compatability. Then again, maybe if linux people would stick with one distribution for more then a year at a time, you might eventually develop an alternative to windows that is a viable gaming platform.
That issue with Linux is that binaries don't always work from one distro to another. I like Linux very much and use it all the time, but the main issue is that the main distributions that most of the others are based on (Red Hat, Slackware and Debian) are not 100% binary compatible. Which is why I'm starting like BSD as all the BSD distros seem to be compatible.
Having said that, some games like UT were released for Linux, so it is possible for them to do it, but Windows makes it easier. I think Linux/Unix would need a much larger market share before most games start to support it. Until then it's dual-boot or emulation.
Right now a lot of people are using Ubuntu, and even some of the new netbooks are coming stock with Ubuntu. Is it possible that games might be developed for this in the coming years?
Not really. Two years ago, everyone was using Fedora. Before that, Red Hat. Linux users simply jump on the next bandwagon when the next big thing comes out, which is a major deterrent for devs (not all linux distro's are binary compatable, so you can't guarentee "linux" compatability.
Its such a small market, it gets ignored as the cost of making a linux game is far more then any potential profit.
Any software that can be installed on one distro can be installed on another distro with the same kernel version as long as it has the required libraries (especially for KDE and GNOME). This lack of "binary compatibility" doesn't really exist, since every file in Linux uses the same byte stream format. The only difference is how it is packaged, be it a .deb or .rpm, and sometimes it uses a universal .tar archive instead.