The thing that kills me is that, at least from reading stuff on tivocommunity, there are a fairly large percentage of Mac users on TiVo. Not to get into the user share debates, but I'd have to think that the percentage of TiVo homes that are also Mac homes is pretty high, and so making an OS X version wouldn't be a lost cause.
But I suppose they really don't make money on TTG, so what can you do? I'd still buy TiVo (I have 2 now) knowing it didn't interface with the Mac (although I miss picture sharing with Tiger).