I read the whole discussion on disc brakes and quick release on Monsieur Brown's website and resolved to check every so often and see if my quick release was loosening up.
It does not seem to be as of yet, but was wondering if there might be several different things happening.
A. Deformation of the nut on the quick release. Over time of this nut being tightened down by the stopping force the nut deforms and does not allow the fastener system to provide the correct clamping force. You tighten it as usual, but it works it self loose on a ride.
B. The amount of force applied to the skewer exceeds the elastic range and will not provide the correct clamping force anymore. E.g. Think of a spring overstreched.
I am not a metallurgist, fastener engineer, or Jobst Brandt.
These are just issues that we were 'taught' about in a recent safety meeting on fasteners.