Didn't they pull this leg with the PS3? Just because they're looking for mac/linux engineers doesn't mean they're actually going to release anything for those platforms. My most likely guess is that they're looking at bringing the Steam platform to the mac and linux, which would make them a fairly decent packet of cash. After all, if they can't be arsed to port their games to the PS3, then they won't bother to do it for the mac or linux, where the gaming install base is going to be much smaller.

Valve Looking For Macerator

So steam, if they can be bothered, nothing more.