I've always found the pushback against 'hype' interesting. You don't really see it as much in other entertainment mediums. If I go to a movie forum I don't think I'd find people wigging out over other people getting excited for some upcoming film (especially if it's within that film's subforum!). Even if that film is overhyped.
What may be different here is that these games take so long to develop and a lot of users here have been disappointed and waiting for something fulfilling to come out for probably going on years now. This means the notion that something they feel is overhyped and deficient becoming successful despite this makes their prospects of a new game coming out that is more in line with their preferences that much worse. After all, if a ''crappy' game does really well, we can expect to find many of its features and designs in future games.
I get that sort of apprehension, but honestly, people are excited again. So what? I think 2012 is going to be a great year for MMOs all around. Even if GW2 ends up overrated or overhyped I'm sure it will still be a solid game and the fact its generating excitement in this genre is a good thing. After the one-two punch of Conan and WAR in '08 it's been a pretty rough last couple of years for the genre. Now we've got all sorts of cool stuff on the horizon!
I can't speak for everyone, but part of my theory is that a lot of users who may not care about GW2 (or whatever game is currently trending) are seeing topics on it constantly on the active feed on the front page and may be annoyed so they come in to participate in the discussion and it sort of spirals out from there. We generally have 'trends' here at the site where regulars from all the other subforums are mostly talking about the same game for a couple of months at a time. A few months ago our stats leaned heavily on SWTOR, now GW2 dwarfs SWTOR discussion. This will likely be the case up to and past the first couple of months of launch, and then we'll all be talking about something else, much to some other group of users' annoyance!
The Forum Circle of Life!