yep that all sounds familiar. BITD most of the lightest rims that I came across were built with spokes that were too thick and the resultant wheels were not especially good IMHO. DS drilling cracking in the lightest rear sprint rims was almost endemic, much as it is with many of the lighter disc-specific rims today.
FWIW I have occasionally built wheels with deliberately well-lubricated nipples, just to see how close to the wind we are sailing; too close and the NDS nipples will soon start to back out in hard use, if the rim is light, the dish large, and the tension balance poor. If the NDS nipples start to back out, then you know that the wheel is about as light/dished/loaded as you can get away with. Threadlock on the NDS nipples can then render the wheel more or less reliable.
BITD folk did all kinds of things; near to me one wheelbuilder would, if necessary, crimp the nipples on the NDS spokes to prevent them from backing out.
In very many run of the mill factory wheels, the nipple threads are essentially unlubricated, and after a period of use, mild corrosion can cause brass nipples to bind a little and stay put on the spoke ends. Cheapest threadlocking possible....
In many 'factory' wheels with minimal spoking, the spokes themselves come with pre-applied (non permanent) paste-type threadlock; the paste contains micro-spheres of locking agent, so won't become active until the nipple is fitted and the microspheres start to break. Later adjustment is always possible, but the reserves of unbroken micro-spheres is limited, so repeat adjustments over time are accompanied by an ever-weaker locking action.
In the PX wheels I've come across with ~20 spokes, the spokes have been of that type; you can see the threadlock (usually blue or green) on the threaded parts of both new and used spokes. Maybe not all their wheels are built with spokes of this sort?
cheers