Okay, here is my theory on why both the opposition and the regime in Iran support Bush. The regime is hoping for a close election that would leave Bush acting like he has a mandate without the actual mandate. Just like the last 4 years, btw. The best thing that could happen to the regime in Iran is a Bush electoral college win.
They would love to have four more years of Bush's rhetoric and the resulting wedge between America and the rest of the world. Kerry is too subtle for them.
The opposition hopes that Bush will have a clear victory that would show American support for Bush's policies. This, they believe, would keep the Iranian regime wondering whether or not they would be the next target.
That's just my theory... no more, no less.