It seems to me that it really comes down to a matter of where things are asked. FB tends to be more optimal for conversations that lead to smaller pieces of information, while the forums tend to get more announcement-y type of responses from Home Office. That’s not to say that FB doesn’t get big announcements or the forums don’t get tidbit responses. It’s just not 100% crossover between the two.
Conclusion: Be everywhere to hear everything! 😀