Some blog platforms whitelist comments from people who have had previous comments approved. I'm pretty sure these meaningless (but positive) comments are an attempt to get on that list.
yes. also some platforms (mostly forums, less of blogs) allow editing of posts, so forum spammers sometimes post meaningless crap only to replace it later with spam.
We should be able to detect that by looking for large numbers of posts with small edit distances. That will contain false positives, but looking for very large numbers should mitigate that.
