I heard several versions of the why there is no "official" mac version. but it centered on the fact they (bethesda) don't like the mac even to this day even though I'am satisfied with the ps3 version and hope Skyrim look fantastic on there. I'll have a sure bet Skyrim won't be on the Mac.
it just I would like to try mods. but personally I don't care wether they do or not, it just they didn't have a clear answer of why.
another thing I heard Havok is not workable on a mac is part of the reason although the modders got around that somehow.