Look at the dates of the unregistered posts - they're all very old. The site was made registrated-people-only a couple of years ago, after some problems with spamming.
Thanks, Michael - yes, spam was part of the reason. Another was that the forum software changed so that unregistered guests could no longer post photographs - so that became less than useful in a lot of ways. Anyway, I think it's working better now with registration required.
