The most pressing problem that the page classifier solves is for the current community of developers using Diffbot. We only offer APIs at the moment for extracting information out of frontpages and article pages (see http://www.diffbot.com/our-apis/). While we'll be releasing more soon for the other page types that you see in the infographic chart, this limitation is a problem if, for example, you're passing in a photo page or recipe into the article API--you're not going to get an article back since its not appropriate. Having the technology to visually understand what the types of pages are allow us to route those requests.
Beyond that, it's useful for companies that perform analytics or use the information to do better search or auto-categorization.