Why can I play some games on second monitor, others not?

[apattee]

For instance, playing Grand Theft Auto: San Andreas, I can choose to play on my second monitor. But for Rainbow Six: Vegas, I can't. I am using Boot Camp. Is there a reason? Thanks.

edit: I have a 2.33 MBP with 256 vram if it matters.

[HiRez]

I've got to assume that some developers have taken the time to write the necessary multiple-monitor support code, and some haven't. I remember when Apple started producing wide-screen displays, it took game developers some time to write support for the non-4:3 aspect into the code, one by one. Some of these games could be fixed to support it later with a patch.