I'm not trying to be pedantic and you probably might already be aware of this, but in one of the examples you gave ("If I don't exercise...") "doing nothing" sometimes might actually be better than doing something. For example, weightlifters who are trying to build muscles are well aware that muscles are not built during training, but during the rest periods between trainings. So in a sense, you could argue that you are ONLY getting more fit by "doing nothing". It would be counterproductive to exercise all of the time and never give your body a chance to recover.

Aside from this small critique, I agree with the spirit of the post and I think it is an excellent point to bear in mind.