I don't know if I should mention any names since it might cause offence but usually, if I don't understand a comment, I have to ignore it
which might seem rude but better than giving the wrong reply.
Some people might not feel comfortable getting into a meaty critique, maybe it comes from insecurities about their level of intelligence (peoples' self image bears no correlation to their ACTUAL intelligence, usually much, much higher than they give themselves credit for).
Maybe they don't want to sound too eager, or talk about their perception of your ideas in case they are wrong (to an extent, I think there is a right and wrong in percieving text), so they put a vague or generic comment. I say 'so what?', at least they read it and felt compelled to comment either way. I'd imagine with most vague comments you can gauge whether they are positive or negative.
Stan's example is a strange one though. I'd definately ask for clarification on that, and if I got a similarly vague or dismissive comment back, then I might just ignore it, or tell them to go swivel.
Oh look, a link. I wonder where it leads.
JoHn
http://www.ukauthors.com
http://www.ukapress.com