This post is an example of how words can go wrong. Richard hasn't clearly specified what this 'model' or 'implicit model' stuff is, yet for the whole post he repeats again and again that it's not in control systems. What is the content of this assertion? If I accept it, or if I reject it, how is this belief going to pay its rent? What do I anticipate differently?

Can anything be 'model'? How do I know that there is a model somewhere?

The word itself is so loaded that without additionally specifying what you mean, it can be used only to weakly suggest, not strongly assert a property.

Any property you see in a system is actually in your interpretation of the system, in its semantics (you see a map, not the territory, this is not a pipe). Interpretation and the procedure of establishing it given a system are sometimes called a 'model' of the system, this is a general theme in what is usually meant by a model. Interpretation doesn't need to happen in anyone's head, it may exist in another system, for example in a computer program, or it can be purely mathematical, arising formally from the procedure that specifies how to build it.

In this sense, to call something a model is to interpret it as an interpretation of something else. Even a rock may be said to be a model of the universe, under the right interpretation, albeit a very abstract model, not useful at all. Of course, you can narrow down this general theme to assert that rocks can't model the universe, in particular because they can't simulate certain properties, or because your interpretation procedure breaks down when you present it with a rock. But you actually have to state the meaning of your terms in the cases like this, hopefully with a definition-independent goal to accomplish by finally getting the message through.