You seem to be confusing the nature of the doctor-patient relationship (i.e., whether the patient contracts with the doctor or contracts with the hospital who employs a doctor) with the use of surgical assistants (generally a type of physician's assistant). Private practices routinely use PAs in the US to do less demanding procedures, just like the UK. Obviously, the nature of the doctor-patient relationship will influence the degree to which PAs are used -- patients generally want full surgeons, while 3rd party payers like the government want to save costs -- but that doesn't undermine zomg's correction of WalterBright's comment.