It's all to do with riding style, I'm 12 stone, and the only thing I've broken on my bike is the spokes, mind you, my bike isn't that light in 2008...
I also don't understand the whole concept behind, "lighter=weaker", look at all the top UK riders bikes, they are all pretty lightweight specs, like Ali C, Stan Shaw, Waynio, Bessell.
But I do agree with your take on the no compromise areas, and an expensive build definately doesn't mean it will ride well.