U.S. Stationed Marines at Barbados Embassy on 9/11

In the VP debate, when Congressman Ryan asked why we had Marines stationed at other embassies on 9/11 but not in Benghazi, Joe Biden asserted he didn't need a "lecture on embassy security" and then went to on criticize the Romney/Ryan ticket for allegedly politicizing the Benghazi attacks.

Problem: the U.S. did have Marines at the embassy in Barbados on 9/11, so why weren't there any in Benghazi?
 
Biden's response to Ryan's question was to arrogantly dismiss the inquiry, then attack the questioner. Step three was then to shift any remaining blame by pointing fingers at the intelligence community and boldly declaring, "We did not know they wanted more security."

But why were there Marines stationed at the embassy in Barbados, and, according to Ryan, a Marine detachment guarding our ambassador in Paris? Why did some embassies and ambassadors have Marine protection but the embassy near which there was an armed Al Qaeda cell had none?

Biden has yet to answer this question.