"Are the Americans punishing us with bombings because Iraq has refused to sign the SOFA?"

Well, we'll know soon enough: Since both al-Maliki and al-Sistani are now both in favor of the agreement, those Americans who are supposedly behind the bombings will at least stop them until and unless the Iraqi parliament rejects it.  If the bombings continue regardless of the current Iraqi momentum towards supporting SOFA, that would seem to weaken this speculation.

But quite frankly, I find this theory hard to believe to begin with.  Mr. Ali, the blogger, is correct:

Don't they realize it's in the interest of the Americans for everything to be quiet right now? That all of this violence actually makes the Americans look bad?

And his colleague Mudhafer's explanation, in that blog post, seems much more plausible:

Mudhafer astutely suggested that the insurgents are savvy enough to understand how this thinking works and could be taking advantage of it to cause chaos.

In other words, the insurgents know that Iraqis are susceptible to anti-American conspiracy theories, and the rationality and credibility of such theories is beside the point when the aim is simply to make people hate and distrust Americans ever more intensely.

Truth unfolds in time through a communal process.