Would you dare an (unverifiable) guess at the percentage of people who plugged in a USB drive to copy some files and were enlightened to use it as a backup unit by the Time Machine dialog?

If I had to, gun to the head, I'd say that no one ever was.

I seem to remember that Windows pops up a baloon in the system tray every once in a while nagging you to configure the system for regular backups. That seems much more sensible.