I don't know what everyone is getting so worked up about, I mean think about all the times your going to "want to sneak up on somebody" and it almost always involves cover or concealment.
The rogue nudges the door open a bit quietly. He sees a guard in the room. He hides (door is cover), and then moves and sneak attacks.
A guard is watching at the front of a castle. The rogue is stationed behind a tree (cover), waits for the guard to move his head to the side, and rushes over and sneak attacks.
If you allow the move from hiding is still a sneak attack, then I don't see the problem.