That's an interesting observation, Garlic. It matches my own experience. I just never thought of it that way.
I walk 3 mph in town, on pavement. On the trail, after a week or two, I think 1.2 or 1.3 is about average
I'm old, so climbing puts me anerobic pretty fast and my speed drops as low as 1/2mph pretty fast for the climb.
It took me FOREVER to accept that "it is what it is!"