What does the competition offer for the price?
I honestly don't know... if other Android phones are offering 64GB versions, you might see that with the iPhone. If just about all higher-end Androids come with 32GB, then Apple won't do it just yet.
There is no other smartphone in existence that offers more than 16 GB internally other than the iPhone. HOWEVER, they almost all offer a microSD slot that allows you to buy 32 GB microSD cards, which means that almost all have the potential of greater than 32 GB on the phone at once. Given that the microSD card is very small and removeable, you can certainly carry an additional 32 GB in your pocket if you want to, for a total of 64+ GB of easily accessible storage. The iPhone does not gives us this option, that's why it needs 64 GB internally to be comparable.
Tony