I do not understand why this is news. All CA (cellular automata) simulations tend to diverge in various ways as they run forward. In fact, the unusual situation is where they have some sort of stability. With the degree to which CA is being used, why hasn't this become common knowledge? All these folks going on and on about "mathematical models" of this or that, and they don't even understand the nature of the math? Huh?

More counter-intuitiveness follows. The more complicated you make the model, oddly enough, the less likely it is to be stable. (I'm looking at you, weather model)

I suspect that differences are random so that on average they are performing statistically about the same.

Oddly enough, nope! Nice try, though. The rate of divergence is unpredictable and not guaranteed to average out to anything. In fact, that's the definition of chaotic. Unless you've discovered an attractor, you just have unpredictable noise. Add that with CA and you have systems that diverge in various ways at various rates. Sure if you're sample size was huge, it'd probably all work out. But 2-3 or even a few dozen? Not so much.