One of the comments that I used to be able to make fairly universally two or three years ago (before virtual tape adoption was widespread) was that your backup is your archive. Typically, unless you had a strong legal, regulatory, or compliance requirement, your tape backup was your archive. And your archive was your tape backup.
This is not a good thing.
Backup and archiving have two wildly different use cases. They store different types of data. They require different retention periods. They have very different characteristics.
One of the good things about backup to disk, irrespective of whether it is virtual tape or disk directly addressed by the backup application, is that we get to rethink backup and archiving. That rethinking usually lets organizations think about what is different between backup and archiving; it is also an opportunity to re-architect, to have two different systems for the two different requirements. After all, when I am down-sizing my tape environment (see footnote) it is a really good time to have the discussion about what I really need to replace it, what my technical and business requirements are, and what I should do to address them.