I'm saying that this is what the people I know who have both degrees are doing. I suspect that most of them did the MBA after practicing medicine for some time and discovering an interest in "management" of the group practice and a desire to upgrade their skills. There is a certain credibility that goes with the MD/MBA such that both the docs and the suits think that the guy at the table understands their point of view.
Whereas most (all) lawyers have had training in contracts, business law, etc. that helps prepare them to be a managing partner, docs who are leaders in a group practice have no such "basic training" and often get the same through an executive MBA program.