i.e. - because they won't get any points for the answers?
Not for me. What discourages me from answering most wiki questions is the 30+ other answers already there.
No. Poorly worded, insulting, argumentative questions or questions with lots of answers already are the ones that don't get (more) answers. I doubt if most people even look to see if the question is CW before answering.
I'm pretty sure that it does play a role in the decision on whether to answer or not, especially when writing an answer would take a significant amount of time, yes.