Simply stupid and counterproductive
It doesn't make any sense to block digital access if they (US) are suppossedly promoving freedom and more democracy around the world (Iran is a democracy, like it or not).
Why? Because the people more affected in Iran should be precisely the opponents to Ahmadijenad, and/or those more 'modern' or westernized.
Again, another proof of the US government obssesion with Iran. As many analysts point out, Pakistan, a dictatorship with 180 mill population, proofs of real nuclear capacity, unstable situation and with strong presence of fundamentalist groups, should be a factor of more concern to US security in near future.