It is useful but it's proprietary and could possibly leverage their own backup drives. Personally, I prefer the explanation that it's there to drive users to create backups. Maybe because Apple knows how reliable HFS+ is ;)
I think skore's point is right though: reminding users to make backups is the lesser evil.
I actually meant both - You CAN consider it the lesser evil while it also has the nice side effect of clearing the market (for simple backup in OSX) from competition as early as possible.
I think skore's point is right though: reminding users to make backups is the lesser evil.