There's an even simpler answer: in his collection of unpublished
manuscripts that we call vol. III of CAPITAL, he simply dealt
with the case that Ricardo had considered, i.e., where profit
rates were equalized. I also think that his assumption that
certain "aspects of capitalism that really existed in order
to tell his story of exploitation (and of profit as being
surplus value)" fits better with his vol. I assumption that
commodities trade at prices equal to value, which in essence
assumes that all capitalists are alike.
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But Jim, why would commodities exchange at value equal to prices and not higer
or lower or some arbitrary way? The word *law* in the law of value stand for
the competitive mechanism. If there is higher profit in one sector then capital
moves to that sector and increases the supply and brings the price down. A
tendency for an equal rate of profit accross sector as an aspect of competition
in capitalism was strongly held by Marx. It is a different thing that perpetual
technical change may keep disturbing the gravitational point, nevertheless the
gravitational point is there. (we keep switching networks but the discussion
goes on!)
Cheers, ajit sinha
