Clark's "Material Surrogacy" 1

It seems to me that much of Clark's paper could have been written simply to show how material culture provides many tools that causally enable us to think things we would not have thought otherwise.  But, near the end, he thinks that the story he has told supports extended cognition.  But, think of his discussion of the way in which surrogates can better help by suppressing concrete detail.  (Here is where you don't really need to have read the article.)  Now, I don't doubt that the experimental work Clark cites supports this kind of conclusion, but what does the additional claim that material culture realizes extended cognition add to the mix?  Not seeing this probably enabled me to read (most of) Clark's paper as being about nothing but the causal utility of material culture.