Okay, I think I understand where you are coming from.
But you do realise that any field in science will have a cutting edge, and at this edge, there will always be unanswered questions.
This is one of them.
Already there are scientists working on the problem, increasing thier knowledge. Here are two links I got from someone who knows a lot more about the topic than me: http://www.ncbi.nlm....pubmed/16983079http://www.ncbi.nlm....pubmed/18648534
So basically, this discussion is going nowhere before the research finds either that epistasis happens, or that it does not.
But I DO want to point out something interesting. I want to point out how you react to the situation. The author points out a problem, and a possible solution. You accuse him of accepting it on faith, where in reality, he is simply proposing a hypothesis.
You imediately assume that the hypothesis is INVALID, despite any evidence for or against it, where the scientific appraoch would be to see it as a possibility, until the evidence rolls in.
Now, this seems to be the crux of the problem.
Why do you imediately think the hypothesis (epistasis as a solution to the problem we are discussing) is INVALID, as opposed to simply waiting for the results to come in?