And I think that MD's are even more conservative.
A large part of patients' treatment comes from their trust of and belief in the doctor. Besides the placebo effect (which is more significant than most think) and other strange psychological things, patients that don't take their doctors seriously might not adhere to the treatment regime, which can undermine the medication.
I'm very liberal and wouldn't care if my doctor was tatted or pierced or whatever, but most patients (especially older people, which make up a huge proportion of patients) aren't prepared for 'hip', 'trendy' doctors. The expect seriousness and professionalism, and physical presentation plays into that. I think, for now, the friendly chitter chatter and small talk should be left to nurses, while doctors should appear wise and competent, not to say that doctors shouldn't be warm, approachable, and friendly.
Thanks @reedobandito for the vest
Warning: Spoiler! (Click to show)