in my own personal opinion... FB is not the best tool to connect on a public web service like a discussion forum. though, it was probably picked over other tools because of its 500 million plus registered user base.
i have mentioned it in the other thread. FB for most people is way too personal. and there are too many things to consider before linking your account to third party sites.
i bet developers here would find good ways to integrate multiple services without cluttering the interface.
essentially. instead of the facebook connect button, they can just have a register button on the top bar. that would lead to the registration page with all the available options... including manual account creation.
even vB had stated that they were going to add other login tools to their own product in the future. they too currently only support Facebook right now.