Maybe?
I dont like to think I'm a lurker, but Attention grabbing titles draw me in, then I read the post and find I either:
a) Have no real interest in the topic
b) Cant post without getting inflamatory
c) Cant think of anything to say.
perhaps your posters already see their opinions expressed, and dont want to post it again, or just dont feel like by that "Ah, I got totally Ninja'd!" person (something I've never quote understood). Then again, some may be like me and have one of the three above reasons, if not another unlisted.
.... ANd of course some just might be lurkers.