Is it the same for official release ?
Of course! Just because you may have a RAID-1 configured on your DNS-323, it doesn't mean you're completely protected.
For example: What if lightening struck your DNS-323? No RAID will protect you from that. Where is your backup? How will you get that data back? How about if a fire occurred? What if both drives failed simultaneously due to defect?
There are many many more reasons why RAID isn't a replacement for a backup. RAID-1 is only purposed to create resiliency in the case of a single drive failure. RAID also doesn't protect against accidental deletion by a user.
Realistically, however the odds of both drives failing simultaneously or being destroyed by natural disaster are amazingly low. But like anything in life, if you take a moment to prepare for the worst -- IF it ever happens, you'll at least have a place to pick up the pieces and start over without losing everything.