Isn't encryption supposed to be a separate layer from the filesystem? Or is the merger specific to Windows? Or, is this ZFS' attitude toward features, like with the volume manager?
Why?
One more addition to other replies: ZFS needs access to disks for self-healing (bit-rot detection and repair). It means that in the past if we wanted encryption, same date needed to be encrypted twice (one for every mirror).
Now with encryption in ZFS, date is encrypted before creating redundancy. We can even do a scrub without encryption key.
Encrypted /home/username filesystem with user-owned keys, is one neat trick,for example.
The ZFS specific encryption IIRC is owned by Oracle, and they do not open source it.