It's widely rumored (with substantial reason) that Amazon MP3 got cut a much better deal from the record labels than Apple. Keep in mind when Amazon's entry first launched, iTunes was practically the only digital music sales service around. The labels were desperate to avoid Apple gaining a unassailable dominance of the market and were throwing other providers significant deals in exchange for fighting Apple. It seems entirely likely that Amazon's normal "cut" for the labels is lower than Apple's.