I don't see it as an issue, especially with the recent announcement of SteamOS, based on Linux. Now developers are going to see extra incentive to develop cross platform games on Linux, because people are going to be buying (or making their own) steamboxes with SteamOS, and if they want to sell their products to those people, they gotta be cross platform. Plus lately, the linux game library on steam has been expanding at a steadily increasing rate.
This isn't going to happen overnight people, but it's definitely gonna happen, and fast. It seems to me like Gabe and Valve are determined to make Linux the new gaming platform. They know Linux with OpenGL has better benchmarks than Windows with DirectX in games like Teamfortress 2, and with a specialized OS to boot... Valve is putting all their chips on this, and where they put their chips, devs will put their chips too.