I have been to the US Embassy in Bogota. It was designed & built in the 90s when guys like Pablo Escobar were running around Colombia unchecked doing things like blowing justice buildings and taking the supreme court of the nation hostage. Therefore, you can see the atmosphere of the time in the design of the embassy building. It is not a regal, statuesque building, nor is it inviting. It is a compound located away from any major throughfares. The walls are imposing, and once you get over the walls, there are large, open fields that are void of even trees. In other words, it would be hard for a large, armed group to approach the embassy quickly. Then, the walls are difficult to breach. Finally, if you get over the wall, the Marines defending the buildings have a large field of fire to cut you down in.
In much the same mindset, the new US Embassy in Iraq is being built. It is first a defensible position and secondly an embassy. Noteably, it has its own water facility and its own water treatment sites. In other words, it can stand on its own.
It sounds like it is being designed to withstand an assault by an force that is not armed with modern armor or air support (I doubt any fixed compound could survive an army with tanks, helos, and jets). Furthermore, with its own supplies of things like water, electricity, etc, it can withstand a long term seige by a hostile forces. It can hold out for a long time until either help arrives or the compound can be evacuated.
One of the most enduring images of the Nam was the over-running of the US Embassy in Siagon by the VC during the Tet offensive. And while they only held the embassy for a short period time, it had a definite effect on US morale and the image of the war. Also, one of the most enduring images of the 70s was the US embassy in Tehran being overrun by Iranians and the embassy staff being taken hostage.
Therefore, I think this new compound is being designed with the realization that Iraq will probably not be a friendly place for a long time and we therefore need to defend our interests. The last thing we need is another embassy debacle in the Middle East that will only encourage our enemies while embarrassing ourselves.