I think it suggests that Facebook is the more personal of the two networks. Twitter is a broadcasting tool — which is why SmartBrief is all over it — while Facebook is less about sharing information or making new connections and more about living your life online — whatever that means to you.
I do agree on Twitter as broadcasting tool. In terms of Facebook I do believe it is about connections with a lot of human touch. And it seems, it will become more and more important as platform for Social Media Marketing, even in B2B.