Premise behind Google AdWords

Yes, there's a big premise. Users have a NEED to acquire a product or information on a product. And hence they initiate the solution via web searching. And hence ads show.

But many times, people DON'T have a need. Or they have to be informed about a need. The need has to be created. In those cases people don't initiate a search. They can only be convinced through an interaction, like sales call or Direct Mail. Or even more broadly speaking, information should be shoved in.

That is why, traditional marketing channels like sales and DM will always exist.

You can also segment any market with this framework. Those who have a need, are aware of it and are looking to satisfy it using the web. And those who don't know about a need. Such segments ought to be closed via other marketing channels.