Meet the new boss, same as the old boss

Comment I left at Randall Beard's blog in response to the question, "Is the New PR really just the New Marketing?":

PR, marketing – these are professional systems that grew up in the Midcentury era. Today these industries are being reformulated to address the huge Millennial impacts of the web, globalization of media, the resulting emerging markets and consumer behaviors. PR and marketing are big industries that carry water for even bigger industries – the castles of the macroeconomy – P&G, Amex, etc. All that structure does not bend and twist easily.

Yet change is the supreme law of commerce. The methods for generating commerce have always been about whatever works. Today there's more whatever and, as noted in your blog post, the mass media have become more democratic. Whether in response PR is functioning more like marketing or marketing like PR, I see this discussion as a snapshot from the evolving art of persuasion. How do we persuade people to buy in the digital age? My question is, what are the consequences to the PR and marketing industries in changing their definition? How does this affect the way they compete?