What people forget is that clients just want to sell more widgets. Sometimes that’s by designing a cool product, sometime is by designing a cool place to sell the product, and sometimes it’s by advertising they both exist.
I’ve met many ux’ers who think the customer doesn’t need convincing once they are at your site, but you always need to sell. And i’ve met many ad people who think a cool bit of media is why demand went up… and not because someone put a vending machine next to an ATM.
They’re all needed. And they all help the client.