It always seems odd to me that Twitter and Facebook are directly compared to each other. At least in my experience (as a user of both), they are totally different services that fill totally different needs.
It's more likely to be the primary social network, meaning the way you stay in touch with your real-life friends, for people who are younger or more immersed in the African-American community.
Also, Facebook has been taking some very direct shots at Twitter lately in the arenas of public and real-time posting.