There is still the chance that data get corrupted between the time the scrub is performed and the time you read the data, so I don't consider scrubs sufficient.
In any case you are right, they should be performed even with ZFS, expecially to test data that is rarely or never read back.
Sure, there can be one error between scrub and read. But assuming RAID, you need errors on two disks. That can happen in a week or however often you scrub, but that's going to be pretty low probability.
You assume that your RAID implementation is going to actually read all of its parity bits from each of the disks, and check them for agreement, before returning a value to you.
