Basically, if you're asking for someone to offer you their opinion on *topic*, and that answer can often be just a couple words, it's pointless. Yes, you asked for "why" as well, but it's just not going to cut it.
Yes, a question can avoid being a poll if it's asking for a factual response, and not a purely personal preference one.
Quite frankly, your question kind of gets answered just by checking people's profiles here and seeing which IM service they have handles registered for.