My first thought was, are you married to my hubby too - but mine is probably an older and heavier (60 pounds overweight) version of yours.

I know all about that mindset and logic and it's driving me crazy. But ok fair enough, the exercise he does probably puts off the worst effects of his weight.
On the other hand, DH is approaching 50 and his weight is taking it's toll already. He gets VERY soar and his knees and back are hurting a lot. I think there is a very fine balance (and it's probably down to the individual and your age) as to how heavy you can get before your weight becomes an actual physical hindrance to your ability to exercise. When that happens you are in real trouble, because your weight is going to slow you down no matter how much you'd like to be active. Controlling your weight then becomes increasingly difficult.
I wish I had the answer as to what to do, but I don't.