The so-called “Google tax”, where an adwords vendor pays for traffic that would have gotten to them anyway, is a long-running problem that most marketers simply pay as a cost of doing business.
To understand the problem, you can simply search for a popular corporate name like “delta airlines” — the “first” result is a paid adword (“sponsored link”) from Delta. Many people click on the paid link, not realizing they just cost Delta some money. Delta very likely knows this but takes it as a cost of doing business — they do want to make sure you go to their site.
These types of problems are a part of any marketers cost of doing business. Years ago, we had the problem of adware pushing affiliate links to sites which a user would have gotten to anyway (like someone searching for “Dell” and getting a popup for a Dell affiliate — Dell ends up by paying a commission to someone they didn’t even need to).
Ben Edelman came out with an interesting piece yesterday which expanded on the problem. If you’re involved in PPC marketing, it’s worth reading his article.