My take and my understanding of this issue is that the FAA exams are generally easier to pass. However, as part of the FAA skills test there is a very detailed oral exam which, if you didn't genuinely know your stuff, you'd fail.
From what I've seen so far of the JAA ground school, it is really only difficult due to the sheer volume of stuff to learn and memorise. If you fixed wing guys thinks a lot of it is irrelevant, think how us helicopters feel!!!
My current profession involved some difficult exams. These were mostly written in order to prove understanding and tried to have some bearing on the real world i.e. we could take in copies of tax tables, Companies Act etc which is what you would do in real life - look it up!! The need for rote learning did not have much emmphasis.
Cheers
Whirls