Yes, everyone (including people logged in with OpenID) should be able to edit comments -- if they can't, let me know and I'll make sure it gets fixed.

And you deserve the public props for all the hard work you've been doing to keep DW spam-blog-free! If we handed out Medals for Conspicuous Volunteer Service you'd be one of the first in line. On the surface it may seem like those accounts aren't hurting anything, because they're just hanging out doing their thing and posting spam occasionally in their own space, but the more of them a site has, the more search engines look askance at all content on that domain. So, you're actually providing a very valuable service :)