I believe it's because Hamilton didn't cut a corner. He overtook off-line on a straight, so he didn't cut any distance at all. Rosberg's moves were aggressive, but Hammy was completely behind him... And if the stewards say Alonso was, too, then there's no foul. You don't have to leave space for a car that isn't there yet, especially if you start moving before the car gets there. The driver behind has the "last chance to avoid". Really naughty, though.