I'm going to come to the defense of Habs fans (and kind of Leaf fans too) just this once. Then after this my contempt and scorn for their terrible choice in teams will return.
But I think it has to do with a couple things. First, those two being original 6 teams with long histories and also in the largest markets in hockey obviously have substantially larger fan bases to draw from. Larger fan bases result in more fans and more ahole fans by default. Plus its ALOT easier to notice the ahole fans cause they are usually the loud mouthed idiots spouting of ridiculous crap like Carey Price is the greatest goalie in the world. All other goalies suck compared to him and he could kick Luongo's Donkey anyday of the week. As opposed to what I'll call the "good fans" (the ones who cheer for their team, are passionate about their team but can still realistically identify and admit to their teams strengths and weaknesses as well as other teams strengths and weaknesses).
Second, up until last years the Habs have had a stretch where they have been mediocre to average at best. Now they have a strong team capable of winning alot more than they lose. And I think it happens with every team that fans become a little louder and a little more Wang when their team is winning. There isn't much to brag about when you lose, but when you are winning thats a whole other story.
Plus winning also brings along that other "great thing". Bandwagon fans. And it my experience it tends to be the band wagon fans that are the loudest, most arrogant, and also most moronic fans of all.
But as it stands, right now the Habs are winning, and with that comes the new addition of louder crazier idiots, many of whom are sure to disappear into the woodwork the next time Montreal is on the decline.