When you've won everything multiple times, broken just about every record going and you've got 500 squillionbillionquadripillion pounds in the bank it must be hard to really put yourself on the line and find that extra 2 or 3% which can make the difference in F1.
I dare say it's a factor, and it's probably the reason he's given. But he'll know as well as we do that he's having accidents which aren't really what he's made his career doing.