I would assume it does count for walls by default. I agree with the palisade call.
For the brick walls I'm not sure, it makes sense that you could either put effort into the foundations of a brick wall to make it stronger, however I think it's questionable that anyone would want to make a brick wall without getting the foundations right... Is leaving stupidity in as a player choice a good thing? Does anyone really need to bang out a brick wall in a hurry? "No time for foundations, just start laying bricks!"
Palisades do not suffer higher decay from being on non stone foundations, brick walls, however, do.
"The psychological trials of dwellers in the last times will be equal to the physical trials of the martyrs. In order to face these trials we must be living in a different world."