If you look at the dynamics, it's this fact that has likely prevented further attacks, in the short term, on american soil more than anything else. It's hard to find nutjobs willing to take on such a mission among the population already present and the immigration crackdown means that it's harder to place sleeper cells for the future. Compare that to England or France, and I think it's pretty clear that they're far more likely to face eager hoards of domestic muslims willing to carry out attacks at home. The 7/7 bombings an french suburb riots seem to hold that out.
Because of this relative lack of radicalization of american muslims, maybe it's time we simply adopted a more isolationist approach to things. Sure, there are plenty of american instillations they can hit abroad, but it maybe time to just lower our profile and let europe take the hits for a while. They're going to be at ground zero of the culture clash but not as long as we're sucking up all the jihadi oxygen in the room. Remove Iraq as a dirka-bot gathering point and chances are they'll spill over Europe, bringing fire and destruction. Then we'd get a good chance to see if European appeasement has a beneficial result without as much invested.