I think a really, really key point here is that in successful revolutions, protestors, the masses, always have a friend at the top. This friend opens the gates to the governing structure, allowing the protestors to access power from within.
The masses seems to have several friends at the top right now in Iran in Ali Larijani, Rafsanjani and Montazeri. The last two names are powerful members of the Assembly of Experts and are reported to be trying to persuade other members of the Assembly top join their reformist team.
Ex reformist president Khatami is also clearly on the side of the protestors.