There is nothing wrong with a retainer model, and I personally think it is an improvement upon the concierge model.
The fee is designed to cover the enormous amount of staff an MD needs in order to service a practice of 2,500 + patient. It is simply getting harder and harder to keep up with billing, refills, pre-authorizations, referrals, phone calls, complaints, billing issues, etc. Obviously there is a lot more that goes into primary care than just a standard E/M, and physicians should be able to afford to pay a staff to handle all of that. The retention fee makes this feasible and greatly improves the patient experience by allowing the physician to provide higher quality staffing and more face time.
I think it is long overdue.