Making profit should be proportional to the amount of work + the amount of money needed for the initial investment to be recouped. With such kind of agreements, Apple can claim money FOREVER on this app, no matter the small investment that was initially needed to created this app. This is disproportionate. It's like if I give you a hammer, and then I claim that in all the houses you build with it, you would owe one room. It's disproportionate, because "building a house" is way longer and more difficult than building a hammer.