I've noticed that David's gained some weight.. mainly about his face, but not that much to be honest.. and he's a big guy!! (height-wise). I think he carries it well.. as has been previously mentioned, he's happy now, he's happily married to a woman he so obviously adores, is enjoying first time parenthood. Leave him be is what i say!!.. 🙂
Plus i read in one of his interviews that he was aware that he'd gained some weight, but he put that down to his wife's pregnancy, and was joining in "eating for two" or words to that effect, but he also stated that he was working with a personal trainer before the beginning of filming for season four.
I like him as he is, people who complain about his weight should just mind their own business i think! 🙂