Again, I am not even close to being an expert on Iranian politics or its socio-political structure. However, what little I do know, I cannot agree with this.
First, I almost always - perhaps more than 99% of the time - agree with Josh Marshall. So when I read his post above, I was really surprised. The clerics in Iran depend absolutely on confrontation with the United States so long as that confrontation does not turn deadly. Since it is very unlikely that the Obama administration would accept any type of military strike against Iran unless Iran attacked US interests or allies first (also very unlikely), then the clerics have an interest in maintaining the current government in power. They cannot afford an opening with the West, much less the US, which would set in motion the gradual erosion of their power. The fact that Obama is not Bush is a great problem for them. They are not used to dealing with rational grown-ups from the US.
Frankly, it costs them nothing and may diffuse a great deal to order an investigation of the election results and process. Time will cool the street and also permit some back room maneuvering to prevent Ahmadinejad from taking his victory too far.
I am inclined to believe that the initial protests against what is now clearly a fixed election worried the clerics enough to accede to the demands for the investigation. Additionally, keep in mind that Mirhossein Mousavi is part of the ruling elite. He is not an outsider by any means, is not the "reformer" the US and EU are looking for - he would just change the tone. Maybe part of the problem is that he is not even Persian - he is an Azeri, although I really have no idea if that figures into the Iranian equation. Nevertheless, it is entirely reasonable that the investigation would be launched based on his request alone - not to mention the other candidates who joined in the request.
So, I can't agree with Josh Marshall. As much as the elimination of clerical rule would be welcome, that is highly unlikely. It would be like asking Israel to cease being a Jewish State or the hope that the ever-shrinking shrill group of right wing Christians in the US would disavow their positions.
The review will, by and large, be the end of it. How the clerics keep a hold on Ahmadinejad is entirely another matter.