The article assumes that when within a RAID5 array a drive encounters a single sector failure (the most common failure scenario), an entire disk has to go offline, be replaced and rebuilt.
That is utter nonsense, of course. All that's needed is to rebuild a single affected stripe of the array to a spare disk. (You do have spares in your RAID setups, right?)
As soon as the single stripe is rebuilt, the whole array is again in a fully redundant state again - although the redundancy is spread across the drive with a bad sector and the spare.
Even better, modern drives have internal sector remapping tables and when a bad sector occurs, all the array has to do is to read the other disks, calculate the sector, and WRITE it back to the FAILED drive.
The drive will remap the sector, replace it with a good one, and tada, we have a well working array again. In fact, this is exactly what Linux's MD RAID5 driver does, so it's not just a theory.
Catastrophic whole-drive failures (head crash, etc) do happen, too. And there the article would have a point - you need to rebuild the whole array. But then - these are by a couple orders of magnitude less frequent than simple data errors. So no reason to worry again.
*sigh*
