It's more likely you are underestimating your corruption because you are not monitoring it thoroughly. If you have thousands of machines, running for five years, you're gonna see corruption occasionally. No FS can truly protect you (but a well designed FS will reduce the probability that a corruption will become a user-visible event).
Of course there's problems with the disks -- corrupt sectors, phantom writes, misdirected reads, etc. The point is that ZFS handles those problems for us.
I won't discuss the nature of the business, but it's unlikely that actual corruption that isn't automatically repaired would go undetected for any amount of time.
