I agree that in The Race to Be First in Search Listings many people lose sight of the fact that a Search Engine lives-and-dies based on its ability to serve valid (valuable) results.
Many times I have tried to explain this to naive business owners who ask me, "How can I buy the top listing in Google?".
Let's imagine, for a moment, a world where your ranking in Google (or Yahoo, Bing, etc) would be based on how much you spend. This is like a traditional advertising sale in Radio, Newspaper or TV. As a consumer, when I used Google for a search, the results would be completely useless to me. I would stop relying on them and they would die quickly.
You would hire any professional (an Accountant, for example) based on their reputation and integrity. Should I trust the management of my money to an accountant with a reputation for cheating?