We've had a fair amount of discussion about what brakes are original on different bikes.
I've been changing brakes on my own bikes for a long time, and also involved with bike swap meets locally.
What occurs to me is the following, which I would propose as a general rule:
People with moderate-priced bikes are unlikely to change brakes unless they have been damaged in an accident.
Reason: By the no-maintenance standards of the People, it is a pain and an expense that is unlikely to achieve much benefit.
"Justification:" Particularly during times of "booms," manufactuers will do almost anything to keep up with demand. Deviations that don't impact perceived quality enough to alienate dealers will be done if it lets them get something out the door. Unfilled demand is a lost opportunity, like a half-empty air plane. Ain't gonna get that revenue back, ever.
Qualification/Exception: Enthusiasts change brakes. Some enthusiasts have moderate-priced bikes. Therefore, don't let your guard down.
Harvey "cynic" Sachs