Mocking the OP and just being a plain smarta$$ and having nothing productive to add, hmmm... now who is being a troll?
To answer the OP's question, I do believe that if you start a thread it is just plain old simple manners to participate in that thread even if the first post answers you question. As for topics where debates is likely, if you started it then you obviously have some intrest in that topic and I only think it natural you would participate.
I also understand that people have lives and forget about post or threads they have made and noone can address every post made, but when the OP comes back into the thread and calls someone a troll, it is obvious they have enough time to at least make a contribution to thread. But when they do that and that don't , thats when I find that that person is being rude.