MickS's answer is the most accurate. The way Q&A is set up, the person asking the original question only gets ONE chance to reply, same as those leaving answers can only do so ONCE. So if you feel compelled to thank those who leave answers, you'll have to do it "in advance" under the question itself OR do a "group thank you" after several people have left answers...OR email a thanks to each hubber individually through HP.
The Q&A section was never intended to be a vehicle for ongoing discussions like in the Forums. It was intended as a way to give hubbers new topics to write about in full-fledged hubs.
If you meant your question to kick start a forum-type discussion, then you should've used it to start a forum thread instead. ;D