Here is more on the stance that companies should hire 1 vendor that can handle all 3 aspects of search (paid placement, paid inclusion and natural). There is also a little shot against the traditional agency who typically handles the paid placement and treats it like a media buy.
"Companies often hire multiple vendors to manage SEM campaigns. One firm, often a traditional agency, manages the paid search advertising spend; another executes an SEO or site-side optimization campaign; and in some cases, a third firm manages paid inclusion feeds into Yahoo!'s OSMX program. There's nothing wrong with this strategy, except these companies often don't — or won't — share information."