am i missing something here?

i don't really understand spam mindsets or motivations that much, but i've sort of got the impression that it mostly has to do with money. but that requires that the comment spam inject some kind of link or reference into the system, right?

late last week, i started getting slammed by comments, all of the "great site, keep up the good work" variety, which contained no other meaningful content as far as i could tell. no url, random email names, bogus IPs. it just started crawling every entry on my site and laying these comments in.

what's the point here? is this strictly malicious? is it for sh|ts and giggles? is it looking for entry points? testing an engine?

it requires, of course, that i start looking at some pretty hardcore antispam measures that have been posted here, since the blacklist can't touch these things, nor can IP denying, or whatever.

but it confuses the heck out of me, and i'm wondering if understanding this nonsense, will help me in thinking about how best to deal with it.

knowledge? thoughts? conjectures?