Hmm
There are probably differences in the way people who are descended from vegetarians for generations obtain their nutrition from what they eat. Although a first generation vegetarian and one descended from several generations of vegetarians may eat the same food, the latter may be more successful in extracting the nutrients necessary for his body than the former. An Indian vegetarian, I come from a blood line of vegetarians. (This is not to say that there are no converts either way). I wonder if this explains why I have not had the protein deficiencies that American/British vegetarians seem to have. For one thing, vegetarians usually consume milk and dairy products like cheese, which are not found in vegan diets. A vegan diet, as indicated in other comments, does not provide any vitamin B-12. However, Ovo-lacto vegetarians have a more balanced diet since they get their vitamin B-12 from eggs. Proteins are not hard to come by for meat eaters, but Indian vegetarian diets include lentils, beans and other food that provide proteins.
Personally, I am a vegetarian not because I have not been inclined to try meat, but because having tried it, I did not like either the taste or the smell of meat. To imagine that others could relish it is a bit disturbing to me, although perhaps acceptable. I cannot claim to be too fond of some vegetarian foods (especially stuff created with an excess of cheese, brinjals and okra) and I guess I can empathize with non vegetarians who cannot do without a regular serving of meat.
There do seem to be benefits in vegetarianism, especially in ovo-lacto vegetarianism. There seem to be benefits in limited flesh eating too (especially fish). If a vegan's belief that he/she does not eat animal products makes them feel good, I am sure that will contribute to their well being too.
I don't know what the hullabaloo is about in this article, given that these choices people make are based not only on nutritional aspects of their diet but also on other things important to them, such as religious beliefs, their partners and what they like and dislike, their ethical principles, and so on. There is no uniquely superior diet, and the diet is only as effective as the human body's ability to process the diet into nutrients, which varies with geography and genetics.