iPhone OS requirements

Marco Arment:

Geeks can pull an old version of an app’s .ipa file from Time Machine, or presumably hack it out of something else. But for most people, there’s effectively no way to get it back. ↩

Or the Trash.

I agree, it might not obvious where to put the file when you find it.

But aren't jailbreakers geek enough to know this sort of file system hackery?