Yeah I heard this before, but no, it is mostly a processing fee. The reality is:

- Developers helped to make Apple the platform it is today.

- Apple had their 30% fee when the App Store was MUCH smaller. It's not like that fee came only after they had the audience.

- Apple will do zero marketing for you unless you are already successful.

- Apple doesn't earn money with the most popular free apps, but still hosts them. They could charge by traffic, by downloads, whatever, but they won't.

- Apple will charge you if you make money in the app. They will force you to use their payment processor if you want to make money.

So, it is 100% a processing fee and everything else either came later or isn't congruent with what they actually charge money for.

Just as an aside, everything here is true of Android as well, and I think the cut was higher (or there were more intermediaries taking a bit as well): I priced an app $1.47 in 2010 so I'd get about $1 on every purchase.