JetHeat: good question - I've been pondering over it for a while. As anyone who has flown with the USAF on exch will tell you, they do things so completely different from the UK it's hard to make a comparison. Lack of flexibility is the biggest difference in training between the two. Believe it or not, the USAF guys can recite virtually word perfect all their relevant manuals, procedures, 60-16, etc. Whether it means anything to them is another question. But that's the point brought up by (TowerDog, I think) - is any of the information gleened on the UK ATPL subjects recalled or much use to your average 744 driver in the middle of the night over Nikolaievsk?
I think not. Most of it is so out of date it's laughable. ("you line up on Narita RWY 16 where the local variation is 12 east; what do you set your DG to?" Seriously - that was a UKATP nav Question I remember bursting out giggling to). So this begs the question - if you know this stuff, does that make you a more knowledgable pilot in today's glass cockpit environment? Would intimate tech knowledge of your a/c type be more relevent? I think so, and on this point the US crews score well.
I've addressed the handling question in a previous post.
Knowledge of the various rules and regs around the world is also important, and on this the US crews are very average. This is partly because the FAA emphasises checking on domestic routes by it's inspectors, probably due to budget constraints. But the big 3 are working dilligently to improve this. Remember, most of the pilots at AA, for example, didn't have ANY Europe flying until they bought TWA's routes in the late 80's. Nugget Euro-pilots are more used to travelling into strange FIR's at an earlier stage.
As you progress in your career, you'll find you recall less and less of the ATP theory, because you don't use it, and mostly it's not relevant. You'll wonder why they ever made you go through a lot of it, and why they let ex-navs set the questions.