It's common knowledge, freely admitted by US military analysts, that the US "way of warfare" focuses on overwhelming fire power, massive logistics and battles of annihilation.
That's what the US army does and does best. That's also what a lot of the senior commanders think it should be doing exclusively.
(There are fears in Europe that the US might develop a mindset where it goes in and breaks heads, and then European troops have to clean up their mess.)
But this is not what the US army is exclusively asked to do, and when it becomes a matter of prioritising resources for training troops for what the army thinks they should be doing (killing the enemy) and what it's asked to do (policing) then the resources tend to go to maintaining the fighting skills.
Which is when US troops in general start to suffer in comparison with the Brits, the Danes etc. (The Italian Carabinieri perhaps being the world's best police troops here.)
The scale of the US deployment in Iraq of course matters as well. Danes and even Brits have the privilege of sending those troops they think up to snuff. The US is carrying the operation regardless.
That this is the state of affairs is completely uncontroversial. It's a matter of priorities and the US army has placed a low (no) priority on this compared to its allies.
Linky:
http://scholar.google.com/scholar?hl=sv&lr=&q=cache:eHSetRq9I0IJ:www.ndu.edu/inss/strforum/SF218/