Hi 411,
Ask yourself the question, if UK pilots are operating in the US, on UK aircraft, on routes and destinations outside the US, what is the problem? The crews just happen to be based their for a short time. The also go to the trouble of gaining an FAA licence, are checked by a FAA check airman.
Oh and just one small point, JMC with an agreement with the US will allow up to three times the number of US pilots to operate in the UK, than have operated in the US. They have been offering employment to US pilots for quite some time now.
P.S Iam not a JMC pilot, but support their actions, and understand their logic.