1. MD's can do more healing than ND's. Diet isn't going to fix a broken leg.
2. MD's are more likely to find work than ND's.
3. I don't know what ND clientele looks like, but MD's are more likely to see sicker people on SAD. For example, the very poor. IMO you get a lot more health bang for your buck by making a very unhealthy person fairly healthy than making a fairly healthy person super-healthy.
5'0" female, 45 years old. Started Primal October 31, 2011, at a skinny fat 111.5 lbs. Low weight: 99.5 lb on a fast. Gained back to 115(!) on SAD chocolate, potato chips, and stress. Currently 111.