They'd need about 240 voice actors for accents to actually work good.
Never mind. You're talking about different races having different voices, right? They already do. They also had different voices in Oblivion (other than Dark Elves).
^
As far as accents go, that makes sense if they aren't all living in Skyrim, which they are. Some could sound more unique I guess if they are travelling from distant lands...
But yes, with 70 voice actors compared to 14 in Oblivion, it would be a travesty to NOT have each race have their own voice actor. No more Nord/Orc, and one elf voice for Altmer/Bosmer/Dunmer... That was terrible.