Or what we see is Palpatine using Unleash for a lot of damage on one turn, and then immediately grabbing the top initiative slot in the next turn to use Move to send Windu sailing out the window. After all, he's enough of a prick to do just that, and it's not too far-fetched to figure that Windu was staggered from a critical injury on top of the Ensnare effect leaving him immobilized, even if just for that one turn. By the time Windu could properly act, he's already been flung out the window to his doom.
We also don't see the Sith trying to simply fling people into the air in the prequels for the simple reason that the people they're facing are fully trained Jedi, who could quite easily use their own Force abilities to mitigate/negate the fall outright. Mechanically, they'd be opposing it with an Athletics check, and probably have Enhance as well for the Force Leap ability, which the GM might factor into the opposed check as well.
We don't see Vader doing it on Luke during either of their cinematic confrontations because he wanted Luke alive to serve as his apprentice and overthrow Palpatine. And by the time Palpatine stepped up to the plate in RotJ, he was pissed off enough at Luke's defiance that he wanted the brat to suffer rather than give the kid a quick and far less painful exit. As for lack of EU examples, Vader (in the EU) is similar to Maul in that if he engages in a fight with a notable opponent, he doesn't just want to win but wants to utterly crush that opponent and prove his superiority.
Edited by Donovan Morningfire