i, Personally, am turned on by how much a woman is enjoying herself....not by how much her breasts sag or how untight her ass is....it is all about the orgasm and the wiggling right before {and hopefully after too!!!} Besides, most guys are so excited just to be in the same place with a naked woman, they don't notice LOL
Tell the wife that bodies are so great because they are all so different. I once had a lovely girlfriend that had scars on her belly from past operations, and she felt the same way. I always just told her that she was the love of my life and she turned me on just the way she was. P.S. it is hard to see the belly when your face is buried in other parts...