Carbonfiberboy 

OK, simple. You overheated your rim and blew the tire off. Not the tire's fault. Same thing probably would have happened to a clincher. You should descend steep grades by letting the bike run, staying off the brakes, then braking hard and briefly for corners, obstacles, driveways, etc. Sit up and use your air brakes. On most descents, terminal velocity is only ~55 mph if sitting up. No fear, just pay attention. I've found that deep alu rims provide the greatest margins descending, as they have more mass to absorb heat and more surface area to dissipate it. Light climbing rims are the worst, too bad.