Sunlover..
Here's an article you may find interesting..
http://www.johnforester.com/Articles/BicycleEng/Wheel.htm
Particularly this paragraph:
Note this paradox: heavier cyclists should have tighter spokes. Since the wheel supports weight by reducing the tension in the bottom few spokes, unless there is sufficient initial tension to more than support the cyclist's weight as amplified by the bumps in the road, the bottom spoke will become loose over the worst bumps. If it becomes loose, the head works and flexes in the flange hole, and the nipple tends to unscrew from the v