Political Economy Arguments
In a coda to Making Meaning ("Film Interpretation Revisited" Film Criticism 27, no. 3), David Bordwell argues that textual interpretation is a skill predictable in its rhetoric:
...[Making Meaning] suggests that within the profession, film interpretation has become routinized. One can quicken undergraduates' interest with critical moves that are long-practiced, but one's students are not one's professional peers.
I don't want to cede the value of textual analysis - nor the ease of teaching it to undergraduates! - but the point is taken that disciplines shift the difficulty degree of scholarship as the field develops. It's no accident that film criticism today usually needs to be put to the ends of a theoretical or historical argument and that single-film readings are not as common as they used to be.
Moreover, though interpretation raises special hermeneutic issues, I don't think it's merely textual analysis that becomes a first order skill readily mastered by those outside the field. Consider political economy arguments about media industries. They're an incredibly valuable model of historical change for film, television, and media historians. I've used a version in my argument that prestige films shift because of economic conditions in the film industry. You can find excellent coverage of political economy work at Alisa Perren's Media Industries blog.
But note that film and media scholars are not the only ones to employ it. Edward Jay Epstein, for instance, writes well-researched but thinly-referenced popular-readership books on the contemporary movie industry. Consider his post on why TV is replacing cinema as prestige entertainment and Alex Tabarrok's follow up at Marginal Revolution. These posts present arguments that are familiar to historians studying contemporary television and film: competition with video pushes cable movie channels to diversify offerings, cable TV is able to pursue quality audiences, etc. In the process these posts demonstrate that media and film specialists don't have a particular monopoly on political economy arguments. (In fairness, Tabarrok is an economist.) I don't mean this as a slight on Epstein's writing, but as a question for what a PhD and research specialization bring to the equation.
But I have a methodological point, too: the political economy approach has its limits. Tabarrok references a "lowest-common denominator" aesthetics of the movies and free TV, which have to speak to a mass audience and sacrifice things like character and dramatic weight. This would explain the relative status of prestige TV v. film (some people like the idea of watching quality programming and "serious" films), but I don't buy it as a full explanation. Classical Hollywood, for instance, had a mass audience and some of the dramatic qualities signaled out as prestigious today. Epstein also notes that international distribution creates this common-denominator effect. True in one way, but that raises other questions. Why can't studios green light both Global Hollywood projects and prestige material meant primarily for a domestic US/Anglophone audience? Well, in fact they do just that, only their attempts (Assassination of Jesse James, for instance) get good reviews but little popular-press buzz. The sociology of reception matters a great deal with prestige product.
In my mind, political economy is best thought of as a fulcrum for rather than a driver of historical change. It effects, catalyzes, thwarts, or exacerbates both supply- and demand-side cultural changes taking place - it can even suggest the relative weight of supply and demand sides of cultural influence. But it does not substitute for culture itself.