Half my bodyweight was roughly 160lbs, that's nearly 4 times what you seem to consider "substantial" so you'll forgive me if I think I have a somewhat different perspective on weight loss than you do.

Besides which, here's what you've missed in your calculations: Precisely because there are lower calorie foods that you can eat, choosing not to eat 500 extra calories is much easier than 500 calories of walking. You can eat three of the meals you described every day (assuming your math is correct, I didn't check) and only consume 1500kcal, right? Since that's bound to be a deficit for pretty much anybody who actually needs this advice, you don't even need to walk at all. You probably should, just don't kid yourself into thinking that it makes up for poor dietary choices.