What behaviors are to IE, bindings is to Mozilla. I love this post, as I am writing after quite some time. All day long I read and studied a lot about these things. Here are some links you might like to check out.
There were a couple of more links but I guess I forgot to bookmark them. Anyhow these links should give you enough information about XBL and HTC.
The concept seem so stupid at first but they really make a lot of sense.