The idea is that when an incline is steep enough, you fall, and it doesn't have to be straight down. It's not so much as a slide as it's falling down and you're hitting the ground on your way to the bottom, if that makes any sense.
I agree though that the physics of the game need to be improved. There's even basic stuff like momentum - why does my character change direction in mid air based on the way he faces?
I think that with the point you raised though, I don't think it's a change in the physics that the devs need to do, so much as a falling animation. If my character falls, he should do a little bit of a stumble or roll. And then Karyuu will post saying "We're working on it! All in good time, it's coming Soon(tm)!"