Perhaps the reason there are more Uk people here is:
(i) Its easier to communicate in a chat room if you are on the same meridian. We pay for our local calls here, so dialing in during the daytime, except at weekends is a lot more expensive. We're five hours ahead of the East Coast and eight ahead of the West Coast and around 10 hours behind Sydney, Australia so it would be hard (but not impossible) to find a good time to chat.
(ii) The boards that I've seem to mention tend to revolve around predominantly US providers, like AOL. In the UK its cheaper to use a free ISP like Freeserve.
(iii) I think a word-a-day has been wold-wide since its inception so has attracted people from all over the world since the beginning.
There is a discussion on the "Miscellany board" about the relative merits of chat rooms versus boards if anyone is interested.