there really shouldn't be a Linux game market, just a game market. I know that's not likely to happen anytime soon and it wouldn't even make sense to most of the businessmen whose decisions could cause it to come about, but ideally there should be only one computer version of the game, alongside whatever console versions might be released. Computers have enough hardware in common, and the three major flavors of OS have some differences but they are not necessarily ones that affect games so much, at least now that most of the larger problems like graphics and sound are largely solved. Why make separate box versions for Windows and Mac when you can just put executables and installation systems for both in the same disc? With a little effort Linux can be added to that mix as well, as open source and indie games have proven - the game content itself is / should be platform independent anyway. It is my hope that in the future OS compatibility will just one of the bullets in the Compatibility section on the back of the box.
Steam for Linux would be like this if they made it, as Steam for Mac shows. If you buy the game for one OS, you can download and play it on the other as well (if it has a Mac version and supports "Steam Play"). I have no problem paying for games (other than having no money) and would pay full price, but it doesn't make sense to have different prices for different platforms. Id Software's games usually get a Linux port, and I've found that a great way to play them. Due to my GPU having been released before Nvidia's initiative to provide updated notebook video drivers, I simply cannot get new drivers for Windows (I dual boot). Since I do get the latest drivers for my Linux install, those games actually run much better in Linux for me - wish I could say the same for games running under Wine.
I realize it's unlikely and with Valve having opted not to get involved, any progress is likely to be slow, but Linux is an enjoyable operating system to use, even for gaming. Linux users pay full price for games all the time - they just usually have to play the games on a different platform unless they are made by Id or otherwise have a Linux port available. I agree that the game companies don't have much incentive to invest in cross-platform compatibility at this time, but as it slowly becomes easier and some companies start to do experiment with it, it will be interesting to see what the effects will be. Linux does have more to gain than the game companies do. The number one reason I hear from people who wanted to switch to Linux but decided not to is that they don't want to go without certain software which isn't available for Linux, be it games or things they need for work. It's hard to judge what effect more proprietary Linux software would have on things like market share. I'd love to find out, because once Linux has more market share, there would be more software available to me (so which comes first, the chicken or the egg? or will I get neither?). In the end, people just want the choice to use the software they like with the OS they prefer, and don't really like it that the reasons they sometimes can't are business reasons rather than technical ones. I may in fact be rambling now, so I'll leave it at that.
-Dan