To quickly recap, App Store developers can charge whatever they'd like for apps -- including free as in $0 -- and Apple will take 30% off the top, from which they pay storage, bandwidth, infrastructure, transactional processing fees, etc. Obviously 30% of free is nothing, but for $9.99 apps, they'd gross almost $3, and net... well, that's anyone's guess. (see above).
I think Liew’s numbers are well below the actual revenue numbers, but no matter if its $50 million, $100 million or $200 million, that’s not a huge amount of money for a company that has nearly $30 billion in cash in the bank. But going forward, that number is only going to increase both as the platform expands and as in-app purchases come into play. That’s not bad for a company that just wanted to make enough money to keep the App Store running.
Parallels to the iTunes Music Store, and what it did for iPod sales, are thus as plentiful as they are well founded.