Well Nintendo is revamping its website for a new look and feel. Perhaps they felt that either:
A) A message board would not really fit in the new vision of the site
B) The design of the message board needs to be changed with the site not only in appearance, but rules for posting.
I don't know why they couldn't have moved the page and disconnected it from the Nintendo main page though and kept it going. It would have made much more sense, and people wanting to chat could still find it.