It is "a" backup but not a "backup solution." RAID (except 0) is for primary local backup. An external drive/NAS could serve as a secondary local backup. No backup solution is complete without off-site backup which should involve mailing *something* to someone else--the farther away the better. It could be a disk, it could be a tape, and it could be a portable hard drive. All of which need proper protection from the elements.
The advantage of having a complete backup solution is not only getting your data back but the closer to home the failure is, the more rapidly the recovery can be performed. If a drive in a RAID array goes out, it takes a few hours to reconstruct it with a new drive. If the RAID failed and you have to copy it across a NIC, it could take many hours. If both those systems failed, you'd have to wait at least overnight for an off-site backup to make its way back to you in addition to some time to restore it.
RAID is simply the first hardware defense against data loss.
Heh, in this case, your RAID made sure the virus wasn't lost.

The good with the bad I suppose.
What do you mean you cannot reboot your PC? All those instructions do is repair the boot files (NTFS/MBR). If the computer was infected, Windows may be damaged beyond recovery. Best to get your data off the drive and do a fresh install.