You are misinterpreting that statement. What they are referring to in the above quotation is when search results are altered due to change in advertiser dollars. Kind of like when Yahoo used to have top advertiser links above the normal search results, and undifferentiated from the content.

Google, as a result, made a separate, distinct location for advertisement links. Because they separated the location of advertisements from the search results, they preserved the integrity of the search results.

This structure has not changed, as you can clearly see sponsored links are separated from search results: http://www.google.com/search?hl=en&q=pizza