Really, it is of no significance to me, as I am not lacking in ways to play them; but wouldn't opening up your products to another market be the savvy thing to do?
Well it's kinda of a win / lose situation. The more platforms they put there game out on the harder it is to support the game because they're could be lots of bugs that you'd find playing on a Mac but on a pc the bugs would be non existent. Which they then need to make patches for as well as hire more people for support. But since Macs have a low number of different hardware types it makes making the patches easier than it would be for Windows in some ways. As everyone else has said tho the Macs are much slower because of the lack of good drivers and under-clocked gpus. Even more of a challenge might be that i don't think the Gamebryo engine is built for mac development, although i have seen a few games that use it available for mac, but I'm not sure of the time it took them to port.
All this being said I highly doubt a mac version of any future elder scrolls game, and doubt even more that we would see any past games ported.
In my opinion mac's are a dying bread anyway, apple continues to make poor business decisions (no flash on I pod touch or I pad being one of them). My hope is tho that Linux will rise up against both Windows and OS X, and we will see Linux versions of all future games.