I'm probably a "casual gamer" these days. I bought two books for 4e, and probably 3-4 for 3.5e.
The reason I'd say WotC should think about casual gamers is there are probably a lot more of them than dedicated gamers. If I can get five people in my group eventually picking up a PHB but not really buying anything else, that's at least as good as relying on me to buy 5 books. Reducing the barrier to entry to the hobby, and the expectation of continued investment, can increase the number of players and make more money.