This is the bit that bowled me over:
I?m tempted to explain this by saying that writing about the specifics of a performance is simply harder than writing about the specifics of a screenplay. However, I don?t think that this is precisely true, that is, I think it is harder for most writers to write about acting, but not because of any inherent difference in difficulty. Rather, writers, being writers, find it easier to treat movies as a piece of writing. They find it easier to write about the literary qualities that movies shares with other kinds of writing (plot, theme, dialogue, etc.) than it is to write about those qualities that movies share with interpretative/performing arts.
Which I think is absolutely true, but hadn’t ever really thought of it before. In spite of my undergraduate wearing of Literature and Theatre hats.
He is very much right about that part.