There are so many NPC's in this game, and a good amount of them have pretty elaborate flavor text each with varied personality and often have little regional stories going on in the background.

World of Warcraft's NPC's with voices just repeat a hand-full of canned phrases that are recycled among it's races.

A better example of voiced NPC's with personality is Guild Wars 2, the base-game of GW2 has so much voiced NPC's going on and about their day, talking with other NPC's, and playing out scripted scenes while a player passes by.

This game does the same thing with it's NPC's that GW2 does, just with text instead.