This is a diagram that illustrates a hub and spoke model for positioning a blog in relation to off-site social networks and media outposts. It's simple and effective.
Blog content provides more in depth, conversational content for more information. It can attract traffic on its own via search, RSS and links.
Rather than pointing links from Facebook or Twitter directly to corporate web pages, pointing them to information on a blog is less abrupt in the (casual to commercial) relationship that brands want with social customers.
The blog as hub also helps focus link acquisition and subsequent search visibility. If emphasis is placed on a mix of social networks and sharing sites without a hub, there's less opportunity for link signals to pinpoint for search engines which content is the best for inclusion in search results. Content from the blog can be promoted via social distribution channels resulting in exposure and the likelihood of organic link acquisition.
If a company has multiple blogs, they would do well to have a blog hub that centralizes blogs as well as other social destinations. Each blog has its own home page and if appropriate, might have its own ecosystem of social activity. Each outpost (Chris Broganism) or forward operating base (Eric Schwartzmannism) can exist reciprocally promoting the blog they are connected to.
Of course, any kind of content should be managed by an editorial plan that is thoughtful of keywords for SEO value.