They wouldn't get paid for the first year of their contract. But they would also get to free agency quicker. And if they all hold back from entering for a year, they could drop from a #10 pick to a #20 pick, and then loose all that cash in in the 2012-13 season due to the lower salary slot.
So if you are a hot name right now and you are possibly going to go higher than you should, you might as well enter. Its the smart financial move.