Watch the making of videos. They tell the voice actors to cram as many lines into a session as possible, changing tones quickly, and thus lowering the quality. In other words: Bethesda doesn't care about dialogue or the quality of voice acting, the only reason its in there is because text-based dialogue won't sell.
Really?
Hadn't seen. I've seen the making of New Vegas vids, and the guys in charge of the voice actor direction seemed very involved. Don't recall the making of vids stating who was directly responsible (shows Avellone, Sawyer, Bergman and the sound board guys conversing with the actors) but they all seemed to take time to direct.
That's disappointing. Extremely disappointing. Infact, I cannot stress enough how disappointing that is to hear that Bethesda just doesn't care about quality, but rather efficiency.

Side-by-side comparison, for those who care:
Skyrim: http://www.youtube.com/watch?v=yJIJ4WevxGA&feature=related
New Vegas: http://www.youtube.com/watch?v=he2h-fgvV5w
Both the directors and the voice actors themselves just seem more personable and involved with the project.