There is a point that is often missed, which is that if Iran's Supreme Leader Khamenei committed a massive fraud, he was not only defrauding the youth who were burning police motorcycles in the streets of Tehran at night. He was defrauding Hashemi Rafsanjani, one of the most powerful politicians in Iran and the richest person in the country.
Rafsanjani is an icon of corruption in Iran. And he publicly associated himself with Mousavi by writing a public letter to Khamenei complaining about Ahmadinejad's bold, and possibly foolhardy tactic of naming him during the debate as a example of corruption in the political system.
I believe that millions of youth in Iran or any country would have to powerlessly stand by and watch a monumental fraud take place in which power is denied to the person who earned the most votes.
Rafsanjani, the chair of the elected Assembly of Experts, which has the power to remove the Supreme Leader, is not a youth who cannot coordinate with others because the SMS system in the country has been disabled. I do not believe Rafsanjani would have to powerlessly stand by and watch a monumental fraud against a candidate he is personally associated with.
If there has been systematic vote fraud, the Assembly of Experts has the resources to find it and expose it. It also has the power to remove Khamenei from power, and further has the power to ensure the Khamenei is punished, including with imprisonment for setting such a fraud in motion. Mousavi and Rafsanjani are both well connected enough to ensure that would happen.