I think some of the Democrats were allowed to vote no on the original bill for political cover, but could be made to vote for the bill as needed. The 220 votes that were cast in favor are unlikely to be the only votes Pelosi can count on.
Well what's changed since then? Town Hall Meetings over the summer; NJ, VA and MA going our way and the Tea Party movement gaining strength in numbers. What makes you think they will now side with a losing majority?