For those of us tracking news from military and other sources, this information has been collecting for some time. Your article shows some examples. Last year, weapons shipments from Iran were intercepted. Travelling on donkeys, no less. These particular items were not of Iranian manufacture, so not much was made of it back then. More recent items are Iranian.

Given the number of times we have been burned on intelligence, obviously the evidence would have to pile up pretty high before it became something the military would want to officially release.

Incidentally, the Iranians have been aiding insurgents and al Qaeda as well, despite religious differences. One of the most pervasive myths out there is that no religious faction will aid another one or a secular one againt the United States and/or Israel. This is not true.

A few more comments specific to the article:

The claim serves the purpose of helping to lay the blame for the whole insurgency at Iran's door.

Only an idiot would try to lay all the blame on Iran. For one thing, Syria has been a major factor since the beginning. For another, a huge number of the bombs and IEDs in Iraq have been manufactured from conventional Iraqi munitions found lying around, not special weapons. Same for mortar rounds, ammunition, and the like. Maybe Iran is getting its oar in now, but they certainly were not essential to the insurgency effort for the past three years.

I have also heard from reliable military sources that it is not all that difficult to create a "shaped" charge from less-sophisticated means, and that special forces are trained in such techniques.

It's not a good idea to try to claim that every high-powered explosive in Iraq is of sophisticated manufacture, either from Iran or anyplace else.

On the other hand, the article's idea that this news serves as a method of applying diplomatic pressure during a critical period of negotiation makes a lot of sense.