Not having read anything, but just in here with two examples of walking to lose weight.
Two years ago, I wanted to lose weight, but at a BMI of about 40, I didn't feel much for most excercises. Going to a gym? I felt like I'd be looked at. Swimming? Yeah, right, in a bathing suit with THAT body? Running? Never liked it, never will. Cycling, no matter how much I loved it, the seat hurt my behind too much so I'd probably go cycling once a week, then recover the next six days.
So, walking it was, together with dieting.
I lost a whole lot of weight! (That I gained it again, albeit slowly but surely in the next two years, is a different story). But my plan was (and again is this time around), to first lose weight, up my fitness level and THEN go back to swimming/fitness once I feel better.
Let's say it like this. Someone who weights 250 pounds that walks 30 minutes has got a lot more excercise done than someone weighing 150 pounds who walks 30 minutes (same pace). Heck, the 150 pound person isn't carrying another 100 pound around! Obviously, as you lose weight, you'll need to intensify your excercise. No wonder you're hitting a ceiling: Every step you take, becomes easier, thus burns you less calories, increases your fitness level less and less. At 200 pounds, walking is still quite a thing to do, but as you lose more, you'll need to step up your game.
As I said, two examples. My dad used to be a construction worker, so he was used of working hard all year. As he got older, what he ate stuck more and more onto his body (before he was one of those zero-fat, all-muscle short guys). But every year we went on holiday, he would make long walks (minimum 10 km/day, which is over 6 miles/day). Lo' and behold, every year, those four weeks on holiday, he'd lose well over 30 pounds.
AGAIN, he was in HEAVY construction, lifting weight all day, working easily 10-12 hours a day! Barely any changes to his diet (well, in construction, he did eat about 5 filling meals, on holidays they became lighter, but there was more snacking, like a hotdog, fries, all kinds of other fat food, so in all, I guess his caloric intake was kept almost on par).
So, can you lose weight just by walking? Yes. But you need to be hauling more than just 5 extra pounds and you need to increase your excercise level as you lose weight.