I think the mix of races is pretty sensible for Skyrim. Lots of Nords, large minorities of Imperials and Dunmer, some Bretons, some orcs, the occasional Redguard. All these hail from places not so far from Skyrim or from countries outright bordering Skyrim - and the Dunmer in particular have a reason why many of them migrated to Skyrim. Altmer, Bosmer, Khajiit and Argonians all come from countries further removed from Skyrim, as others have said, and hence are rarer, although not completely missing. I understand that the Khajiit fans and Argonian fans might miss their favorites, but it's logical that they be rarer in Skyrim.
If they have a game set in a southern country - Valenwood, Elseweyr or Black Marsh - it would be logical to see plenty of Imperials, Khajiit, Bosmer and Argonians, but fewer Bretons, Nords, Redguards and maybe even Dunmer and Altmer.