I still count it. Today I just did a little mile and a half with my wife and (slow)dog. It was in the sunshine and I was moving. After the AFC championships I plan on doing another walk. You can try jogging to a lightpole and walking to the next and jogging a lightpole etc... to get the heart rate up(I do this on occassion but mostly to stay warm in the summer I hit mountain trails). I too try to get the 55% heartrate but if you can't get it at least half the time you may have to pick up slow jogging, or intervaljogging, or pretend you are hauling a carcass and carry a bag of sand around.
But seriously that kind of deters from t he rejuvinating purpose of a decent walk..