I agree that that there are some forums, such as this Suggestions forum, where Discussion may be the more appropriate choice. The people who contribute to this group know that, and usually make the Discussion choice. But it does not really matter if they do not.
But for the average topic forum (e.g. the Visual C++ forums that I hang out in), Question is almost invariably the correct choice, and most uses of Discussion are novice user error. This has serious negative consequences for the OP, because some responders will not bother with a Discussion thread.
In some previous version(s) of the forum, the Question/Discussion choice was made by a drop-down, and there was an even greater prevalence of incorrectly chosen Discussion choices.
If you want to go back to a situation where there is no default selected, I think it is essential to have some kind of pop-up for the Discussion choice that emphasizes that you should not make this selection if you are expecting any kind of answer to your post.
David Wilkinson | Visual C++ MVP