Also, it would be inadvisable for the staff of such exchanges to travel to (or transit through) the United States. http://en.wikipedia.org/wiki/David_Carruthers#Arrest_during_...
The reason why those P2P-style exchanges aren't common in the United States is because it's hard to directly transfer money between two people. With SEPA transactions in Europe you can directly transfer money to any recipient, usually for free (or at a very low cost).
[1] Instead, they can sue you locally, even if they crime happened in another country. However, this lawsuit will be according to local laws. So if the crime is only illegal in the other country they can't sue you.
Can you elaborate on which countries do you have in mind for "comply with the local laws, which are often much less strict in terms of AML provisions" ?
For extradition you mention Europe, but the EU AML directive is already comprehensive enough to make illegal most suggested bitcoin-for-laundering use cases; and it can be expected that if there are major loopholes found, then (continuing with their existing AML policy) EU legislation will be quickly adapted to close them.
Also the US is not the world power anymore. They have no authority to 'flag' any currency.