All of this misunderstanding of the GPL aside, this is an entry on the Mac app store, i recall a great deal of fuss about certain requirements on programs sold from said app store to restrict the user's freedom in ways that are fundamentally incompatible with the GPL.
Long and short, you _can_ sell a GPL'd game, no problem there*, you can't, unless something's changed that i'm not aware of, sell it in the mac app store, it's against apple's terms and conditions.
*assuming the whole game including data is gpl'd, this is rarely actually the case with games that use ioq3 and i'm fairly sure trem's no exception.