Brand Equity & Forcing the Brand Buy
Yahoo! put out a research paper highlighting activity bias, stating that the efficacy of online advertising is often over-stated because people who see ads about a topic were already more closely tied in with that particular network & that particular topic before they even saw the ad. As an example, any person who sees an AdWords ad for hemorrhoid treatment was already searching for hemorrhoid-related topics before they saw your ad (thus they were in the subset of individuals that might have came across your site in some way if you were in the search ad ecosystem or not).
This sort of activity bias-driven selection bias (homophily) exists on social networks online & offline.
Google did research on incrementality of ads & they came to the opposite conclusion as Yahoo! did. Google suggested you should buy, buy, buy, even on your own branded keywords. They suggested that testing was expensive (no mention that the only reason it is expensive is because Google chooses not to make such tools easily accessible to advertisers) & that the clicks were so cheap on branded keywords that you should buy, buy, buy. Many advertisers who mix brand & non-brand keywords together don't realize that they are using the "returns" from bidding on their own brand to subsidize over-paying for other keywords.
Google Analytics is the leading & most widely used web analytics program. They can share whatever metrics help them sell more ads (defaulting to crediting the last click for conversions, even if it was on a navigational search to your site) & pull back on features that are not aligned with their business interests (SEO referral data anyone?)
This goes back to Scott McNealy's quote: "The only technology I’d rather own than Windows would be English. All of those who use English would have to pay me a couple hundred dollars a year just for the right to speak English. And then I can charge you upgrades when I add new alphabet characters like ‘n’ and ‘t.’ It would be a wonderful business."