PR:ROI or reputation?

Whilst conducting my research I managed to get caught up in Epiphany Solutions blog frenzy regarding PR vs. search engine optimisation (SEO). It made me wonder how relevant ROI actually is in regards to a PR campaign. Sure, it all depends on a clients aims and objectives but I was taught PR is primarily about reputation. Should PR professionals be expected to demonstrate direct impact on the bottom line? Is that there job? More importantly, is this holding the industry back?