It has been argued that the washer was left off in order to get enough threads into the nut to achieve 30 pounds of torque. The same argument suggested that custom studs should be made that are slightly longer (4mm) in order to accommodate a washer in this location. The same stud could be made a bit longer where it goes into the alloy to help achieve the torque without tearing out. It's common to find Helicoils in this location.
There are old threads about this somewhere.
Good question.Can the head be removed while in the bike with the longer stud?