Your comment and the poll internals of hispanic and black voter show us what we've always known. There are at least two wings of the Democratic party, the economically disadvantaged and social conservative wing, and the latte liberal wing. The former will vote for Obama to preserve their entitlement and safety net programs. The latter may also vote based on such a rationale, but also heavily favors a progressive social agenda, which the former does not.
It's sad that Obama +22 only translates into +5 for No on 8. This says that a significant number of Obama voters are siding with Yes to H8.