If it's quality enough to warrant my turning off the subtitles, then yes. If I'm just going to read what they're going to say, and skip the voice-tracks, then I don't care if they're in or not.
However, it seems as though having a huge, beautiful next-gen game that has silent NPCs kind of steals from the experience. I like it when they talk, just not when they svck.
Edit: grammar, plus a small addition.