70 voice actors for Skyrim doesn't mean 7 per race. If every race did get 6 voice actors minimum then it would be really awesome, even four is cool. But
rest of the cast are only voicing
individual characters(with minor overlapping).
In Morrowind, most actors voice 2 races with only one actor voicing 3 races. In Oblivion, that's 3 with one actor(same one) voicing 4 races. Yes: shockingly, Oblivion has less voice actors for different races. Morrowind doesn't assign same actor duo to more than one race but in Oblivion one duo voices 3 races, one duo 2 races, another again 2 races. This is an insane overlapping, that's underestimating players' perceptions.
Funny how Oblivion actually got worse. It is worse plus the burden of full voice acting left uncompensated. Double facepalm worthy.
Skyrim has no overlap(off course except within the same race). But still follows 2 per race formula(Except Nords), male and female. We still can't talk about diversity here.
An improvement over Oblivion but I think full voice acting change is still uncompensated. Morrowind has very limited voiced dialog, one fifth of Skyrim, maybe even less and voice actors are only doubled from Morrowind. So it can be seen as under the Morrowind standards.

Sources:
http://www.uesp.net/wiki/Morrowind:Voice_Actors
http://www.uesp.net/wiki/Oblivion:Voice_Actors
http://www.uesp.net/wiki/Skyrim:Voice_Actors