Jeff talked about that on the latest Jar video, IIRC. How it would be ideal from a Wiki point of view to have "every trailer ever". But it's too much of a technical hassle to import all that stuff from Gamespot (not that they have every trailer, but still).
Also I have no problem with them uploading some trailers, and it seems like a silly minor thing to get worked up over.
edit: I also watch pretty much every trailer they upload, and think it's a good way to get people to discuss it. I more or less never visit any other gaming site anymore, so get my trailers from GB (and the forum) and GAF. Should be a way of filtering them out from the front page for the people who don't care, but it's such a minor thing.