... This is plainly not true. First, the ease of finding a bug in a web app varies considerably. This article, for instance, was simply about resending requests quickly. It doesn't necessarily require amazing intellect to come across such a bug. Look at famous "hackers" that dicked around with querystrings and got into all sorts of fun.

Second, even if someone is smart and figures out how to solve a certain problem to gain root, it does not mean they're clever, aware, or dedicated enough to maintain opsec. One mistake, any time, and you're toast.