@pleonasm - People don't just exercise to burn calories though. And health experts are always changing their minds about the benefits of one exercise or another. But I seriously doubt that anyone will ever prove that walking has no benefits as an exercise because it's obviously not true.
You've got to remember that it's usually not a choice between running and walking for most people. It's a choice between walking and not walking. If everyone made an effort to walk for half an hour every day, the world would be a much fitter place. It still wouldn't be perfect, but it would be better than it is at the moment.
And that's the best thing about walking, I think. It's almost effortless compared with other kinds of exercise, but it can help you in a lot of different ways.