At least the download does appear to be fixed. I'm able to download it now, too. Whether it will actually work will have to wait until the download finishes.
That said, the PC version works just fine in Crossover Games through Steam. So consider that an alternative if the Mac version refuses to work.
I'd like to hear your comparison of Steam Mac native versus Steam on Crossover.
I'm miserable working on Steam native. Bought Civ IV Complete Edition on the first day of launch. Downloaded fine, then I had real problems with vanilla and Warlords crashing, but Sword worked. Now I can't even launch any of them.
FFFUUUUUUU!!!!!!!!
It's very frustrating. I had high hopes. Now I am paying to be a beta tester.