Because that's what history has shown to happen. It's also basic politics. If anything, I'm being completely unbiased here. I don't have any stake in the issue nor do I pretend to care about people who have no impact on my life. You guys on the other hand have no evidence to support your assumptions that this change is going to be for the better or if there's going to be any real change at all. I'm sure you all WANT it to be a good change, but you can just look a bit further to see there's no real difference at all regardless of who won the elections. You may choose to believe it or you may not, it doesn't really matter to me.
By saying you believe this election won't matter, you've already formed an opinion about the nation and at least it's rulers, if not it's people. You're calling the rulers corrupt and interchangeable, and calling the people idiots for not seeing what you apparently can see. I'm being overly harsh with that, but don't pretend being aloof and cynical somehow makes your opinion unbiased.
Further, you believe this election doesn't matter because you don't know who the people vying for power are. I don't usually give a flip about Ahmadinejad's rhetoric, precisely because it's just rhetoric. Iran's President has no real power over foreign policy, only domestic policy and trade rights. That's how Ahmadinejad got elected in the first place, promising to get inflation under control and put oil money in the people's pockets. He failed at both of those, but spun enough nationalism to maintain the support of uniformed patriots. (Americans will note the incredible irony here.)
The man probably replacing him, Mousavi, was Iran's last Prime Minister trough the 1980's, during the ungodly destructive and expensive war with Iraq. He had no military power, he was just charged with paying for it. And with America and Britain embargoing Iran's oil and maybe planning to topple the government (again), Mousavi actually managed to improve the GDP over what it was before the Revolution.
As if it isn't clear, it's the Supreme Leader who really runs the military and foreign negotiation. Ayatollah Khamenei was Khomeini's heir apparent (don't let the names confuse you), and has proved himself an egotistical, myopic ass through his entire reign. He has a lot of powerful enemies with more religious clout, and his belligerent, schizophrenic control of this election and response to it has brought all the detractors out of the woodwork.
Khamenei's principle opponent, Montazeri, has enough supporters that this firestorm could probably see Khamenei ousted, and maybe even Montazeri replacing him like the multi-million protesters have signed on for. Why all this matters is that both Montazeri and Mousavi are strong champions of racial, gender, and economic equality. No, neither of them are particularly fond of America or Israel, but they're both pragmatists - these are the guys who kept Iran afloat in the 1980s when people like Khamenei and Ahmadinejad threw it over a cliff. They want to negotiate with the world and be a respected, not feared, country again.
We'll all know in about an hour how things will proceed from here. Right now, Khamenei is giving a national Sabbath address, something he only does a couple times a year. In it, he can only really say one of three things-
-Yeah, that election was all screwed up. My bad, let's try this again. Big smiles people.
-Everybody just calm down and wait a few weeks, we'll count some votes and get this sorted out.
-Praise be to Allah for my pal Mahmoud's reelection, now get your asses home before you're all shot.
Options 1 and 3 can only play to the favor of the protesters, because it would either just give them what they want, or inspire even more support since most of the police and military have threatened to desert en masse if ordered to violence. Option 2 is just stalling for time, which might let things cool down, but when literally millions of people from every class and society are spending every day in the streets in solidarity, there is no room for compromise.
UPDATE: Khamenei went with Option 2. Guess we'll have to wait and see what happens.BIGGER UPDATE: Early reports were mistaken! He went with Option 3! Everyone get your popcorn!The irony is, if Ahmadinejad had just given a few more speeches and Khamenei left the vote alone, he probably would have been fairly reelected anyway.