I'll start by making a partly-facetious, partly-serious point about this very interesting paper. The authors pitch it primarily as an analysis of why fashion has a low-IP regime, rather than whether that regime is optimal. Many of their arguments do in fact amount to a claim that many players in the industry (if not necessarily the industry as a whole) benefits from a regime in which imitation is largely unconstrained by IP law. But they avoid--almost deliberately, it seems--any discussion of whether society in general is better or worse off because copyright doesn't seriously protect fashion designs.
That strikes me as a bit of a shame, because their analysis of induced obsolecense seems to fit nicely into another classic theme in political economy: how an industry can sometimes arrange its market to its own benefit but to the detriment of society. The fashion cycle is perhaps the classic example of wasteful social behavior. We spend enormous amounts of money, time, and grief on things we'll throw away the instant they start to go out of fashion a few months (or even days) from now. Raustiala and Sprigman are hip to this set of arguments; they have the cites to Thorstein Veblen and his "norm of conspicuous waste" to prove it.