this should be in Consumerwatch.
Secondly, this daft, penny-pinching idea is standard practice - the "mysterious" partition holds all the Windows XP files, and it's hidden so that you don't feel tempted to format it, or fiddle with essential system files.
Restoring the computer will have the effect of returning it to its factory state, and that's common practice as well.
Nothing whatever to do with 3-card tricks.
As for backups - backups of what?
I'm moving the thread to Consumerwatch now.