Doesn't it have a lot to do with what wheel it is, type of spoke, design, etc? I've got a set of Ksyriums which have 18/20 spokes and I weigh 210. Another manufacturer, Soul is rated up to 210 with 20/24 spokes and one 20/24 set rated up to 265lbs.

I have a buddy with Rolf Vigors 14/16 spokes. He has over 5000 miles on them and weighs 220lbs. He owns a bike shop and will not ride any other wheel but Vigors.

I'm curious on this subject too, because I'm considering Souls.