yes there are diffrent studies out there. I believe as i wrote in my original post your Body adapts but i am not sure about the "after burn effect". It is intresting though. I still believe you can get great results from say 45 mins Walking. i do however believe 30 mins interval is so much better for Overall health. I feel great after a hard 30 min bike interval in the gym...i like to mix it up with a run in the Woods.
the major problem with it is that it cuts into recovery, whereas the walking doesn't cut into recovery so much