There are plenty of dropouts at every step. Probably the biggest drop-off is the PGY-1 year (internship). That's when you really find out if you can cope with clinical medicine. Staff physicians only want interns and residents to do the scut work they don't want to do: in house call, dis-impacting old ladies in the ER, etc. If it wasn't for the parts that suck, they would assure you they can handle the hospital without residents just fine. I suppose that's why teaching hospitals consistently deliver better care: because the staff can do everything just fine. If it wasn't for parts that suck.