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.
People who go back and downvote every post or comment a Less Wrong user has ever made, please, stop doing that. It's a clever way to pull information cascades in your direction but it is clearly an abuse of the content filtering system. It's also highly dishonorable. If you truly must use such tactics then downvoting a few of your enemy's top level posts is much less evil; your enemy loses the karma and takes the hint without your severely biasing the public perception of Less Wrong's discourse.
(I just lost over 200 karma in a few minutes and that'll probably continue for awhile. This happens to me every few weeks. Edit: I mean it's been happening every few weeks for a few months for a total of only three or four. Between 400 and 700 karma lost total I think? I don't mean to overstate the problem.)