Your whole premise is that "casual gamers" aren't capable of making any kind of decisions, let alone actually playing more than one game at once, and will be fooled into thinking WoW and Diablo 3 are the same kind of game, despite having next to no similarities. The people who you call "casual gamers" are just people who play this particular game less than you do, or in a less "hardcore" way.
Real casual gamers aren't playing WoW, and won't be playing Diablo 3... because real casual gamers play free puzzle games or fucking Facebook games... maybe they have a Wii, but that's it. You're using "casual gamers" as a thinly veiled insult, and for whatever reason, a group of people who are incapable of making decisions on their own.