zlacker

>but it seems highly unlikely that bots using faked user agents create such a large number of impressions that Google has to use this route against them

Clickfaud makes the frauders money. There is a financial incentive in fooling Google's bot detection. There is a lot of bets using a faked user agent.

>Websites can refuse service unless you install their proprietary data collection agent. Websites can refuse service if you use the wrong browser

Websites can already do this.