I imagine that most people who come from here and go to a MUD are more likely to go to the MUD if...
A) It's high on the top 20 list.
B) It has graphical ad banners.
C) They are experienced MUDers and already have an idea of what MUDs are out there.
Nass' post seemed like it could be largely accurate - many MUDers do tend to carry "baggage" or whatever their very strong internet personality is with them from game to game. They are typically not as loyal as other gamers, and more likely to stop playing. So there is always the issue of the quality of gamer (which for many, can make or break a MUD) - are they eager to learn and become part of an online world, or does their ego force them to seperate themselves? Some players do more harm than good, unless your purpose is to make money rather than an agreeable, tight-knitted online community. Though it is possible to do both, as some games have shown.
As far as the questions in the post; they just seem like they'd be impossible, even for Adam, to answer. I imagine that you get a few honestly new forum users sometimes - I know I finally cracked and started posting in forums back in January, simply because it's easier than logging onto everyone's MUDs and chatting/arguing with them there.
Beyond that, I'm sure the traffic is mostly contrived for the purpose of getting in the top of the lists.
When I BETA tested one of my company's new MUDs a couple of months ago, we stayed at the bottom of the Top 20 list near the beginning of a voting term, and near the middle of the Top 30 after that; I did notice that because we were a new MUD, advertised strictly for its unique and dominating PvP Combat - our ratio of votes to traffic received from TMS was about 1 : 2.5
So, in summary - it would seem that most of it is for bragging rights, but that given the right circumstances, one could use the voting as a way to get new players. Graphical Ad-Banners are, simply, far more effective, though.