[davidmanze]

What would you call "calibration" ...... are you saying that Canon or Nikon would offer a calibration service?

Both do, yes.

   I take it you are talking about calibrating a lens on a reference body ........ without any disassembly?   
This basically amounts to "the standard zero offset"   (offset being amount added or subtracted to the norm).
 
  The whole point of AFFT is that you don't have to return the lens to the manufacturer because he has an exact mirrored AF scale within the camera's menu ....... two in fact, one only accessible by the manufacturer ......  the other by the user ..... so whether you offset the AF within the camera or the lens it's the same. .......
 A hacking program could access the Pentax K5's actual AF calibration menu and in there was found exactly the same AFFT as was in the camera's menu ....... so in effect there were two scales of adjustment ... both could offset the other!

 I wouldn't return a lens for calibration unless it could not be corrected within the AFFT facility.