Mike,

You are right for a perfectly smooth surface at a microscopic level.

However that is also ( in my case at least) that is an unachievable ideal.

There is a physical bond as well as the chemical and it is this that the discussion centres on. That bond arises from the epoxy "soaking into" the suface of the substrate. It does help the bond. The question is kinda like "when is this too much of a good thing".

So, if you get a piece of 1/4" soft balsa, and put a coat of laminating epoxy on it, the cut it in half after the epoxy has set you could be able to see how far the epoxy has penetrated. Again the question is "how useful is this?"