The discussion about more basic questions on Server Fault is currently going on at http://meta.serverfault.com/questions/465/perception-of-purpose .  One complaint is about Server Fault being "Developer Support" which it really should not be.  It is a place for professional system administrators to answer questions of other system administrators (regardless of level it seems so far). I am guessing that might have been Jeff's reason but I can't say for sure.

As far as people setting up MySQL on Super User they do it all the time. It is used for the backend of things like MythTV etc.