Maybe there's a convergence of shared interests across all advertisers that serves to create a culture of consumption? I don't think it's that hard to explain or that it requires the positing of any sort of conspiracy.
Not to mention, advertising often has been used to create markets out of thin air:
http://www.theatlantic.com/past/issues/82feb/8202diamond1.ht...
How advertising causes high rents in San Francisco?
Be my guest.
While consumer culture certainly includes sales, it's also about deeper things such as associating your identity and self esteem with consumption, the way those ideas intertwine with culture, the psychological structures through which those ideas are mediated, and the way it all congeals into a way of life.