Disconnecting a USB device shouldn't cause wake from sleep

I find this scenario annoying:

1. Connect an iPod to a Mac. Sync.
2. Hit the Eject icon for the iPod in iTunes.
3. Leave the iPod physically connected to the Mac—it needs a charge.
4. Put the Mac to sleep. Wait.
5. Disconnect the iPod.

What happens next? The Mac wakes from sleep. Because I disconnected an ejected iPod. I cannot think of a use case for that behaviour.