Haven't really thought this through yet. But writing it down might clarify it for me.
I wanted to take a bit of interesting marketing orthodoxy and challenge it.
What I think I mean is that it's rare that advertising creates something new.
It takes a messy, nebulous bit of culture and makes it simple and understandable.
Yes, it can speed up cultural change, but it doesn't create cultural change.
A few examples:
Apple: Think Different (Apple's hard core users came from the creative industries)
Dove: Real Beauty (feminism – stereotypes of beauty damage women's self esteem)
Nike: Just Do It (people who participate in sport have more get up and go)
Omo: Dirt Is Good (mollycoddling kids doesn't do them any good)
Lynx: The Lynx Effect (boys want to attract girls)
Bored of this thought now.
Next.
Influence without logic 
There are two schools of thought on this, either advertising as a shaper or a mirror of culture. Advertising, along with the media are usually a shaper of culture because they teach society about what is and is not of value, how things are done, what to support, etc. Originally when consumerism began after the industrial revolution, advertisers had to create markets for their goods. They did this by telling people that they needed products to fulfill their needs. For instance, before Kellogg’s advertised their cereal as a good breakfast food that aided in digestion, cereal was not a commonplace breakfast food. Now for many Americans breakfast=cereal.
Good stuff Thom. As advertising stops being informative it takes on a role as reflector of culture. My point overall is that in the world of brands (veneer that provide parity products with additional value) advertising teaches culture what’s of value by reflecting back the interesting bits that already exist in culture.