Looking at it now, it seems almost silly not to have one.
Seriously, what would be the big deal? Would one more forum really make the place that crowded?
Xbox has two separate forums. Playstation has three. We're not asking for a new forum for every Nintendo product, like the other two companies already have, just one forum will do.
They're quite right about the Catch-22.. I for one hardly ever read the General Gaming forum, I'm more interested in the specific consoles I have. Which, interestingly enough, are a PS2 and a Gamecube. I'm sure quite a few people also avoid the General Gaming forum for the same reason. That forum, by it's very nature, is non-platform-specific, meaning that people don't want to post platform-specific threads there.
Case in point, I'd love to post a question about Gamecube titles, but I get the very real feeling that very few people would see it, much less read it, much less reply, if I put it in General Gaming. The last thread I put in there, which I thought was a pretty good one, got only one reply.
While you may think there's no reason to put up a Nintendo forum, there's really no reason not to. It's not like a Nintendo forum would kill GTP or something.