Take for example, the introduction of a devastating virus. It does so by placing a break in the stream, by taking the backup physically off line. Put your data out of reach. Only by keeping multiple generations of data on tape and shipping them to a remote location can you be fully assured that you are protected from viruses, sabotage, human error, and other online attacks that a mirrored system does not protect against. The bottom line is that while it will take a little longer to recover using an older generation of data, your company will be able to recover.
Schools conduct fire drills regularly.
And the drills aren't simply to keep the kids in practice. A good recovery plan requires the same attention. Do the drills. Find the weaknesses in your plan. And don't point fingers.