A few minor clarity/readability points:

1. The second paragraph opening "The statisticians who discovered the nature of reality" reads rather oddly when taken out of the context of "The Fabric of Real Things".
2. When considering the three causal models of Burglars, Alarms and Recessions, tackling the models in a "First, third, second" order threw me on first reading. It would probably be easier to follow if the text and the diagram used the same order.
3. Perhaps giving each node a different pastel colour would make it easier to follow what is changing between different diagrams.

And this has probably been said, but using exercise and weight is probably distracting, since people already have opinions on the issue.

All in all though, a great article.