This is true, but there are steps between the two. It would certainly be possible to, for each query, record both the first time and the fastest time. You could also add a couple queries that are a little harder- a query with a self-join and a window function would certainly be interesting- without getting too far down the road of building a query set that will be hard to run on different systems.

Even without those though, this is a good read, thanks for it!