Well, that'd be an idea, but it puts the decision cost in the hand of the content creators instead of that of advertisers. They suddenly have to make decisions for what products are appropriate for their audience, or more likely, what'll result in the largest cut. They won't neccesairly be much more efficient at it either.

And it won't neccesairily lead to less obtrusive advertising.

Useless products seems a little harsh, since a truly useless product wouldn't survive for long. You might view them as useless, but then a high schooler might not know what to do with a cisco rack, and say the same thing. Which means cisco shouldn't advertise their products to highschoolers (for the most part).