The Obama administration had maintained its support of President Ali Abdullah Saleh in private and refrained from directly criticizing him in public, even as his supporters fired on peaceful demonstrators, because he was considered a critical ally in fighting the Yemeni branch of Al Qaeda. This position has fueled criticism of the United States in some quarters for hypocrisy for rushing to oust a repressive autocrat in Libya but not in strategic allies like Yemen and Bahrain."
Saudi Arabia had seemed to give up on Yemen, and didn't send troops or tanks, so maybe the US sees the writing on the wall.
Concerning post-Saleh plans:
"At a State Department briefing recently, a spokesman, Mark Toner, was questioned on whether there had been planning for a post-Saleh Yemen. While he did not answer the question directly, he said, in part, that counterterrorism in Yemen “goes beyond any one individual.”
And of course the US will try to make sure the new government will allow drone srikes of AQ.