It should be a choice, really.
If I play the strong silent type for my main, I wouldn't want to have to do ALL the talking. Let the more charismatic companion be the face of the party and take care of unimportant small talk and roll those skill checks.
I actually like that NPC's can initiate dialogue with anyone because it's more realistic that way, but there should be a way to change character for both dialogue and skill checks.
