That he can slit four thousand throats in a single night, of course!

(I know it's supposed to be a Hun or Mongol quote originally, but the Klingons co-opted it the same way they co-opted Shakespeare, the thieving bastards...)
I think the goal of 4e is to remove all "action-removing effects" a la hold person's nerfing in 3.5, and this is one example that I really don't know if you'll ever see altered even in "greater sleep" or whatever. They want to give the critter or PC at the very least one die roll to do in a round, to end the effect if nothing else. At the very least, a party that's ready for it can make great use of this, assuming there's still a delay type action in the round:
count 20: the rogue delays
count 18: the ranger delays
count 15: the wizard casts sleep; two enemies go down.
count 14: the rogue and ranger pop the heck out of two sleeping enemies, and maybe get lucky enough to kill them. If they're really lucky, they were within 5 feet and coup de grace them! Of course, this assumes coup de graces work similarly...