I can understand your point, but it needs to be subtle. For example, Oblivion's beggars: why do they all sound like old (wo)men, regardless of how young they are? They were a bit too exaggerated, and it sounded out-of-place.
And then they switch voices, and sound like any other NPC all of a sudden ...
And then they switch voices, and sound like any other NPC all of a sudden ...
Exaggeration isn't what I'm looking for but any voice actor worth their salt can make two characters sound different from one another.
One of the films I'm looking forward to the most next year is http://www.youtube.com/watch?v=xivQ6_gu3W8 It's a documentary about voice actors, and you can tell how much they know about their craft.