http://www.poker-tools-online.com/icm.html
Put in 1500 for 10 players and fill out the prizes and note everyones equity.
Change player 1 to 3000 and player 10 to 0 and see the difference. You gain a few %.
You're right in that you still have 1500 chips out of 13,500 as before but since 3 spots pay it helps you out. To see the difference, change the payouts for spots 2 and 3 to $0. Now when a person busts all of his equity transfers to the person who won the chips and everyone else stays the same.