Boondocks also doesn't have the following that Avatar does for one simple reason: Boondocks is a Cartoon aimed at adults. There's a reason why its shown on Adult Swim on the Cartoon Network.
Avatar is aimed at a younger audience, and there fore has more exposure and has a bigger audience. It also got its slot in the Series Discussion sub forums because (like deodaclan18 said), the community showed a significant interest, and there was enough discussion on the boards to warrant it getting its own section.
The fact that the section its in being named "Anime Series" does not mean that AO considers it an Anime (In fact, the majority (if not all) of the staff including myself either don't consider it one, or just don't care).