I think there is more of a fluke factor here than anything else. There is always some proportion of a product run that will fail unexpectedly, and some circumstance that will be damaging way out of proportion to it's apparent force.
I don't weigh 265 anymore but I did and hit a rock hard enough to blow the casing on a Schwalbe marathon. I suffered no damage to the Alex rim. I had 35 mm tires and 85 pounds in the tire. I think lighter pressures run an excessive chance of the impact making it to the rim and either failing the tire, or in the extreme, the rim. I just bought some Dyad 40 holers so I hope they work out. Lacing them with butted wheelsmith spokes, and White hubs. Anyone know the number I should look for on the spoke gage?