I suspect the same thing. Actually I think there are a couple of biases - the name brand association you describe and also an affect I have noticed in myself where I feel inclined to upvote posts that have been upvoted a lot. Following the herd I guess.

If a "famous" poster who regularly accrues a couple dozen or more Karma a day just from popular comments they post would post for a few days under a pseudonym (but otherwise do not post any differently then they would have done) we might get some data about the former affect as you describe it.