Why heatsink pads for only the PIII?

I just got the swiftech heatsink that I ordered to build the computer. I was reading the directions on putting the heatsink on the CPU, and it supplied me with four cussion like pads to put on teh CPU. The thing was, the directions said only to put the pads on a PIII and not P4 and AMD. Why is this?

well amd already has pads on it so adding more would make the hs not make contact correctly and i think the p4 has a heatspreader so it dosent need any pads at all

Oh okay, I was thinkin' that's what it probably was. Thanks!