bbPress is a standalone product, similar to WordPress MU and WordPress.org. The idea is to keep everything modular, and allow people to pick and choose what they want to use.
I think that the way that the Forums are implemented into BuddyPress will change once BackPress because a more mature API.
In the meantime, the forums work almost exactly like the wire does, but for groups instead. Groups also have their own wire, so in reality having a forum is a little redundant until someone takes the initiative to introduce some more functionality into the BuddyPress forum area.
I ended up dropping bbPress all together tonight. I’ve got respect for everyone who’s developing it but it progresses too slowly and SimplePress is a lot more advanced right now, particularly for non-technical end-users. I ended up just installing simplepress and getting rid of group forums until bbPress adds more advanced functionality or the community takes off and pumps out additional plugins.
Personally I’d like to see Automattic acquire simplepress and merge the two products.