It was ultimately Blizzards shift in policy from "its okay that some people won't see all the content" to "everyone has the right to see all of the content" that is to blame for how the game is today. Sure id say that casual players didn't help with all the demands to see and experience all the fruit wow has to offer w/out having to put forth any real effort or learn the intricacies of their class in the process.
So what we end up with is everyone expects to get everything every patch, and see everything whiles its current regardless of how much or little you play the game. The game itself has very few true challenges unless you go out and look for them, and as a result the game does a substandard job of properly teaching players how to be effective in a non LFR raiding environment.
I think this video does a good job of highlighting some of the issues that arise with the new overall game philosophy Blizzard has: http://www.youtube.com/watch?v=9zLP-ugJP7g