There are (expensive) workarounds to data-at-rest for such systems, such as Seagate's Self-Encrypting hard drives which, once unlocked, make the encryption transparent to the operating system, but if the drive ever loses power, data is inaccessible until unlocked (e.g. by booting a USB stick). Personally, I've only ever seen hardware encryption at enterprises which had already suffered at least one significant breach, though I suppose the truly paranoid might have had measures in place and I had no need to know.