I never really got the distinction between those moves in terms of what can learn either.
Sure, Rock Slide feels less like a precision move (in that it's just hurling a load of boulders at the foe) but Stone Edge is described as "stabbing the target from below with sharpened stones". That suggests an additional degree of precision, but... they're rocks. Hell, I could pick up a handful of rocks right now and a couple of them would probably be sufficiently sharp enough to stab with. And it's not as if most of the Pokemon which get Stone Edge are specifically noted for being precision warriors (I'm thinking of Gallade or Throh or Sawk here) - Gigalith, Nidoking, Golem, Coalossal, Steelix, Muk, Darmanitan, Quagsire, Tauros, and even Shuckle learn it.
Sure, Rock Slide feels less like a precision move (in that it's just hurling a load of boulders at the foe) but Stone Edge is described as "stabbing the target from below with sharpened stones". That suggests an additional degree of precision, but... they're rocks. Hell, I could pick up a handful of rocks right now and a couple of them would probably be sufficiently sharp enough to stab with. And it's not as if most of the Pokemon which get Stone Edge are specifically noted for being precision warriors (I'm thinking of Gallade or Throh or Sawk here) - Gigalith, Nidoking, Golem, Coalossal, Steelix, Muk, Darmanitan, Quagsire, Tauros, and even Shuckle learn it.