I think Mac OS X with it's *BSD base has opened up a lot of possibilities for cross platform gaming, not to mention the extra publicity for the open source libraries.
I've got quite a large selection of Mac games and of those most of my respect goes to those companies who have released multi platform discs. Blizzard and Cyan (the Myst guys) to name a couple.
The ScummVM project helped to point out to folks that the same game files could be used on many different operating systems (and I loved being able to dig out all my old PC adventure game discs
One of the financial downsides, of course, is that you need a much wider testing plan. So I'd just like to put my hand up now for any Mac alpha releases TTG want to throw out there.
Please release for Mac... we'll buy them!