I'm going to guess that part of this came from the pages and pages and pages of forums about how much people hated that their hero sat there with a blank stare during funny, sad, or angry dialogue.
Dunno ... there seems to be people bothered by the fact that they might have to hear a line they just read ... personally I would
enjoy it because after reading it I might enjoy hearing how a voiced PC would
deliver it with whatever particular flair or affectation .... but anyway.
Unvoiced PC does not have to remain expressionless. There's no earthly reason why after selecting the line,
"Alistair! You are a douchebag who annoys the living crap out of me!"
Even if I don't hear the line I've just selected from unvoiced-protagonist, my Warden couldn't suddenly adopt an expression of anger and make an angry gesture in his direction. So even if I don't hear it, I could at least "see" him "act" it out.
My point is, yes, I don't enjoy the often blank expression-less Warden, but an unvoiced Warden doesn't have to lack facial, kinetic, and other emotional expressions.
And frankly, it was far more odd how he lacked expressions in
cutscenes, particularly how he didn't even crack a
smile when Morrigan came to bed him one last time....