I'm confused as to how being able to talk breaks immersion, or in your day to day life do you sign, rather than speak?
Characters past Elder Scrolls games didn't exactly have varied response options. It's not like adding voice could limit the choices any more.
Think of a friend or relative's voice... In RPG's you can think of your character's voice, and it is exactly as you wish it to be ~Unless it sounds like one of the guards, or the annoying fan. :laugh:
No voice means two things. First, it means that the player can imagine whatever voice they wish, and second , it means that the developers can re-write the PC's dialog at will, to fit a need, and not be restricted to what was recorded.
*Its also the case that many players read to the end a lot faster than a speaker takes to voice the dialog; and would prefer just to skip to the next block of text, than wait for the NPC to catch up.
The game Arx Fatalis did a great job with their voiced PC; but the PC was a Caucasian male (only) and had a choice of just three faces ~and only one voice.