Think people are failing to see that iOS is a new model, it comes free with the device for starters and you usually get 2 major upgrades for free as well.
Have you looked at how much a copy of Windows costs? That's why Microsoft doesn't need to chase Amazon for payments when it sells books on the Windows Kindle application.
iOS also has a very easy app delivery and upgrade infrastructure.
That automatically makes it different from desktop OSs. iOS devices are closer to the console model.
Now, looking at consoles if you try to put your App in Xbox, Playstation or the Wii you'll get a huge upfront joining up bill plus a commission structure that makes 30% seem just like an add-on option. They also don't allow anyone else to install stuff in their machines, even to going to extremes like Sony. Free apps? You'd be laughed at.
So Apple is already quite open in what they allow.
So the devices, iOS itself, the marketing, app store system, and of course free app delivery is all infrastructure that these companies ride for free.
You can claim that these products also help Apple sell more devices, but one can also argue that what Apple's offers also has value, and in a fair agreement they should also be compensated.
To just ask not to include a link is IMHO a very generous offer.
I'd like to see what would happen if Apple asked Amazon to let them sell iBooks directly on the Kindle.