Most of those Indian vegetarian diets were developed before modern sanitary food processing was. Flour and other processed grain foods in India used to contain significant amounts of insects, which upped the protein content. Consequently, vegetarians who then moved to Britain often became anemic or protein-deficient, as the sanitation standards for food were higher.
I wish I had a reference for this, but I can't find it. It might have been in "Eat Fat, Lose Fat" but I don't really remember.