First, Warsh says that Romer "initiated a far-reaching conceptual rearrangement in economics" by expanding the normal public/private goods distinction into considerations of rivalry and excludability.
Romer is great, but no - he didn't do that at all.
Then a page later Warsh backtracks a little and says that "public finance specialists had used a series of often confusing terms to explain the source of 'market failure'" before Romer (really? these are confusing terms used by obscure specialists?), but even then Warsh claims "it was by marrying nonrivalry to the concept of excludability, and applying the distinction where it had not been employed before, that Romer cast a new light on the ubiquitous role of ideas in the economics of everyday life".
It's fair to claim that Romer applied these ideas in areas where they had not been applied before... maybe... although of course he had predecessors in Allyn Young and even Paul Krugman (brace yourself: Krugman did not get the Nobel Prize for trashing Bush in the New York Times, no matter what your favorite bloggers told you). But it's still not right to say that he was the one that "married" nonrivalry and excludability into something a little different from a public good.
Next Warsh tried to explain exogeneity this way:
"These background conditions were, in modern parlance, treated as being exogenous to the economic system. They lay outside the model, treated as a 'black box' whose detailed internal workings were to be willfully ignored. Exogenous to her concerns is what the waitress means when she says, 'It's not my table'."No, no, no! The first part is fine but that last sentence completely misses the point! Something is exogenous if it does
None of this matters all that much and I'll probably still learn a lot reading this, but it's frustrating to see these sorts of mistakes in the first couple pages!