Most people who are using a search engine are doing it for research purposes. They are generally looking for answers or at least to data with which to make a decision. They're looking to find a site to fulfill a specific purpose. Someone doing a term paper on classic cars for their Automotive History 101 class would use it to find statistics on the number of cars sold in the United States, instructions for restoring and customizing old cars, and possibly communities of classic car fanatics out there. Companies would use it in order to find where their clients are, and who their competition is.
Search engines are naturally drawn to research-oriented sites and usually consider them more relevant than shopping-oriented sites, which is why, a lot of the time, the highest listing for the average query is a Wikipedia page. Wikipedia is an open-source online reference site that has a lot of searchable information, tightly cross-linked with millions of back links. Wikipedia is practically guaranteed to have a high listing on the strength of its site architecture alone. Wikipedia is an open-source project, thus information should be taken with a grain of salt as there is no guarantee of accuracy. This brings you to an important lesson of search engines — they base "authority" on perceived expertise. Accuracy of information is not one of their criteria: Notability is.