It might not be 30% now, but there is a fee for all media content on the iTunes store. If you buy them through Amazon, that split becomes 0 for Apple.The 30% fee doesn’t apply to media content in the iTunes Store.

Apple looking to change 70/30 iTunes revenue split for media services
Apple is planning a departure from the long-standing 70/30 iTunes pricing arrangement it has with digital media companies, reports the Financial Times. According to sources familiar with the matter, Apple is discussing new commercial terms with a number of players in...

You know you've backed yourself into a corner and now moving goalposts.