Actually, encounter powers (or, to avoid the constant misunderstandings, powers that are regained after a short rest) are regained after a short rest. If the PCs do not take a short rest (which is usually assumed to take five minutes), they do not regain their powers that are regained after a short rest.
Which doesn't really make a difference - any smart party will just add "short rest" at the end of every fight. (Which is realistic - you don't press on without catching your breath).
Essentially, the "short rest" limit only added the possibility for the DM to occasionally interrupt someone's short rest with a second fight that was than harder than usual.
I would rather see powers that recharge on time passed - this could go anywhere from "every three rounds" abilities like the early dragon breath definitions (which then somewhat found a PC reflection in 3E's Tome of Battle and its ways to reset maneuvers) to one that recharges only after several hours.