I looked on steam and both are listed as windows only, im assuming coz they aren't 64bit for mac. if you buy those games and are running an older OS, can you download the mac version, is it just hidden from the sales page, or is it gone completely?
Steam _always_ list all avaiable platform versions no matter what and if you buy the game you _always_ get all versions available at once.
If it's not mentioned on the Store Page it's does not exist (on Steam) and you won't get any other versions. It can happen though, that a dev adds a platform or stops supporting one at their discretion.
Also, there are always System Requirements listed at the end of the Store Page for the platforms supported.