Backup ... is backup! Backup ensures that when you accidentally deleted at file, you can find it and restore it. So using RAID and backup are really orthogonal issues.
I'm not sure I agree with you.
You're claiming that RAID is not a backup because it can't save you from deleting a file. But no form of backup can ever save you from deleting a file!. If you make 50 backups of a harddrive and store them each in different places around the world, and then you go to all 50 locations and delete the files (accidentally or otherwise) then you're just as screwed as you would have been if you'd done the same thing with 50 HDD RAID setup.
I'm sorry, but what you are talking about is not doing backups in my mind.
When I say backup, I'm talking about professional level
backup is where you on a regular (and automated) basis copies your files to separate destination media (tapes, disks, optical media, whatever), and allow you to go back a number of days/weeks/months to find snapshots of your deleted file.
It can even allow you to restore the entire filesystem (disaster recovery), should your IT room be destroyed by fire or (more likely) water.
This is backup to me and I would say that if you talk to anyone involved in professional IT operations, that they'd say something quite similar.
Again, RAID is only designed for and can only protect you against failing drives within a storage system (be it JBOD, NAS, SAN). This is why doing regular backups of your data is orthogonal to having a reliable filesystem (and this is where RAID comes in).
For an end-user at home, I do understand why RAID and backup gets mixed up - you just want your data to be safe, and both RAID and backup seem to to that thing for you.Sidenote:
Now, if you go and create a file (e.g. take a picture) and go and by error go and delete that file before the backup system has had a chance to do a backup that file, then ... well, then you loose out.
Been There, Done That. Didn't Bother With The T-Shirt