It is not a matter of the quantity of traffic, but rather "quality" of traffic.
If G determines that most of your visitors are not likely to purchase the products and services offered by advertisers, you can get tossed into Smart Pricing. AdWords conversion rates apparently are a major factor, so if you have a lot of clickers but few people placing orders on advertisers sites, that is one of the major triggers for Smart Pricing.
"It's inexcusable for scientists to torture animals; let them make their experiments on journalists and politicians." -Henrik Ibsen