This isn't restricted to open source project leaders, or even open source developers. You'll find the same childish elitism in pretty much every field of human endeavor. Programmers certainly do it. Laughing at noobs and being mean to them is pretty much the sole purpose of IRC, unless I'm mistaken. Surfers do it. Climbers do it. I've even seen rocket scientists do it. The interesting thing is watching which members…
I think it has to do with the level of mastery. At some point, when you become really good at something (almost anything), you realise that a lot of your own knowledge now comes from explaining the basics to people who don't know anything. By forcing yourself to redo the basics, you get fresh insight on a level that someone new to whatever activity simply can't appreciate because they don't have X years experience wi…
It's pretty difficult to explain things well and be a jerk at the same time!
(although my pope-hat's off to those that manage to do both ;) )