Does anyone know?

Im taking a stab at this one. Top doctors like H&W are backlogged for months with HT's so unless they think that the US can provide a better lifestyle I doubt they will be moving anytime soon. I was thinking the same with Ron Shapiro I figured it would be more beneficial if he practiced in NY or Chicago which would be easier to travel to. But because they are so good, people would just travel to where ever they are.

As for a business decision if any of the top doctors were to setup in the UK they would make a killing. There is no one in the same league as the coalition in the UK or Europe. They would pretty much have this market all to themselves.

Maybe it's due to malpractice insurance costs?

I think the some of the very best clinics are the very best because they typically concentrate on creating one great clinic with one large and loyal support staff. These clinics are well worth the travel.

Those clinics that try to spawn sattelite clinics (i.e. mini mills) normally encounter quality control issues.

I expect H and W, the SMG and other leading clinics to stay focused on providing one outstanding clinic.