I think that his point is to make a distinction between "profits" as remuneration for contributions to production (the know-how, organizational skills, leadership skills etc.) and "profits" as rents i.e. windfall earned as a result of monopolistic control. The latter is exploitation, the former is not. So to the extent as the entrepreneur's income is the remuneration for her contributions to production rather than rent - it is not exploitation. I think it is an analytically sound point worth serious consideration, albeit to make it (if that is indeed his intention) Brad seems to beat too much around the bush to my taste.
I also think that Brad's second point is that Marx's theory of value obscures that distinction, and therefore its analytical usefulness is moot. I am not an exegete of Marxist holy scriptures so I cannot tell off the top of my head whether that charge can be supported by the balance of the Old Man's writings. However, I look at his writings not as an infallible prophecy or iron laws of the invisible hand, but as very clever pastiche constructed to put the received wisdom and ideologies built on it on their head, critique them by reducing them ad absurdum.
Bourgeoisie used the economic theory as a "managerial ideology" to ennoble themselves and their contributions to economy and society. Marx used the same theory to debunk these ennoblement efforts and portray them as parasitic crooks, which many of them in fact were. Bourgeois ideologues portrayed the new world order as the unprecedented achievements in human civilization. Marx debunked that myth by using their own assumptions to show internal cracks and contradictions that could lead to a catastrophe.
Internal criticism is the most effective form of criticism and Marx used such criticism rather well. The fact that some of his pastiches and critiques could be shown to be not particularly well suited to solve some analytical problems? That is disingenuous critique based on double standards akin to debunking evolutionist theory on the grounds that it has some hypotheses that cannot be shown to be factual certainties.
Wojtek