It's a bit off but in the ballpark:

  Google's 2007 study found, based on a large field sample 
  of drives, that actual annualized failure rates (AFRs) for
  individual drives ranged from 1.7% for first year drives to
  over 8.6% for three-year old drives

http://en.wikipedia.org/wiki/Hard_disk_drive_failure

Memory, of course, has other problems:

http://www.ewh.ieee.org/r6/scv/rl/articles/ser-050323-talk-r...

Haven't you experienced it? My HDDs all wear out eventually... there's only so many times a thing can spin 7200rpm just nanometers off the ground before something gives.

I'm guessing this is with MTFB rates given by manufacturers. With continuous use, it's not that uncommon to for hard drives to reach EOL fairly quickly.