I'm not sure that analog sources can be relied on to be present in all systems. And I'm not sure that your other suggestions (stray network packets or uninitial

I'm not sure that analog sources can be relied on to be present in all systems. And I'm not sure that your other suggestions (stray network packets or uninitialized memory) can be relied on to to be sufficiently random in all systems. It seems to me like they're looking for solutions that rely on the processor for the randomness and not on any peripherals.