If you look at older platformers, and even many later ones for other platforms and even the NES, there is typically no "momentum" and "realistic" physics for the main character that you control. Even "Mario Bros." (the arcade game, ported to NES) uses very strange/primitive physics.
I've long wondered: does Super Mario Bros. for NES have the "realistic" momentum effect just because they were the first to think of it and/or have the skills and/or desire to put it in a game? Or does it actually require some kind of "expensive" mathematical calculation which earlier (arcade) hardware simply didn't live up to? And the NES was simply powerful enough to be able to accomplish this?
It's pretty strange if you think about it. It's almost unique to the Super Mario Bros. series of video games, really. I always assumed that other developers simply weren't as good with math/physics or that they were just sloppy developers and didn't take the care to give their game a realistic/"genuine" feeling to how you control the guy.