OK, to the OP, I've thought about this quite a few times, and I think I created the best metaphor to explain why "hardcore" gamers have such disdain for "casual" gamers, or at the very least the surge of casual gamers ever since the iPhone and Facebook came out.
Imagine for a moment you're, let's say, a Basketball player (Or Football, or Baseball, or whatever, just pretend you play a certain sport). You've played it all your life, you've become something of a pro. You probably even play on a local team; you're not planning on making a career out of it, but you are sufficiently skilled. One day, some 300+ pound man walks onto the court carrying a basketball that you can immediately tell he just bought, like, two days ago. He immediately walks up to you and tries to pretend he's just like you, like he's been playing basketball all his life, and he wants to play with you. You know you were just like him at one point, but you were like him YEARS ago, as a kid, while this dude's trying to get in on it as an adult. He's not exactly bragging about his uber basketball skills, rather he seems to enjoy bouncing the pretty orange ball in front of him and throwing it in the air, without much care whether or not it makes it into the net. The sheer fact that he has the gall to consider himself a member of something you enjoy, something with which you have a strong passion for, that he takes so lightly, just infuriates you to no end.
Now, unless I'm mistaken, a lot of casual gamers are playing casual games with no real goal to progress further. A person who only owns an iPhone or iPad, even if s/he has a veritable library of app games, is probably not going to purchase a gaming console and try to work their way up. They're happy where they are, playing the games they play, but when they see someone playing on their DS or PSP, or god forbid an actual home console, they try to associate themselves with these gamers, and it's rather infuriating only because of the world of difference between the two types of games.