A contradiction

Back in April, Google announced a set of new advertising policies, among which was allowing advertisers to choose which sites display their ads. However, this new capability potentially shuts out a "long tail" of publishers which may be:

1. Sites with objectionable content.

2. New sites without a track record, or unfairly suspected of generating fraudulent clicks.

3. Sites with low nominal conversion rates, either due to low real conversion rates, or to low enough traffic resulting in zero conversions over some time periods.

This is part of a more general contradiction: in the quest for "quality" traffic, how much of Google's revenues will actually remain intact? If you take all the junk traffic out of the equation, will we see the same revenue growth rates? Add this to increasing competition coming from Yahoo and AskJeeves and it's an open question whether GOOG's high multiple is really justified.