$5.5 billion paid to developers is 70% of the total raked in, which is (5.5/70%) = $7.85 billion. 30% of that is about $2.4 billion.
It's a fantastic market Apple provides for developers, no argument there. My point is only that it's a very good little business for Apple. Personally I think 30% is a bit rich--20% or 25% would be fairer. But Apple dictates the terms--developers don't exactly have a choice if they want to develop for iOS.
You are confusing gross with net. They have considerably expenses in running the app store.
I made no claims of net vs gross... but if their curation and hosting costs are even close to $2.4 billion, they're doing something very wrong!
Apple makes good money from their App store. Their earnings report for 2012 Q3 states they've paid (cumulatively) $5.5 billion to app developers, which means $2.4 billion in commissions to Apple--hardly chump change. It does look small, however, in comparison to the outrageous profits they rake in from hardware sales.
However, Apple has indeed managed to broadly slash the perceived value of software, a neat way of squeezing Microsoft. MS has seen the light, and it's why they're also going the ecosystem/integrated hardware/software route.
It does give pause about what the state of open computing will be in ten years...
"Most people would like to be delivered from temptation but would like it to keep in touch." -- Robert Orben