Math.SE is a place where users are willing to teach. Math.SE (along with StackOverflow) helps virtually anybody, sometimes to newbs without any hint of clue. Our people won’t engage in pointless quibbles and use high-rep privileges to debase authors of questions (although answers, certainly, require competence). Contrary, people help these, sometimes clueless, authors to make their content eligible. Also notable, this meta site doesn’t have a tradition to shut legitimate issues up, as far as I observed, unlike most other ones in SE system.
Many other StackExchange sites have a spirit of “elitism”. Sometimes it is substantiated by actual expertise of active participants. Sometimes it doesn’t rely on anything but a couple of enlisted celebrities (such as Gerard t’Hooft and Peter Shor at physics.SE), who cover up generally awful and amateurish level of discussions. AFAIK any of “elitist” sites hasn’t professional-level achievements remotely comparable to ones of MathOverflowMathOverflow. IMHO superiority attitudes common at many such sites will eventually undercut their usefulness for anybody but a narrow circle of “professionals”, actual of self-perceived. At math.SE it will not happen.