Malcolm Coles spotted an interesting change in the Google's ranking algorithms. If your query includes the name of a company, an organization or any name associated with a website, many of the top search results are pages from that site. For example, a search for [apple ipod] returns 7 pages from the apple.com on the first page of the results.
Google confirmed this change: "We periodically reassess our ranking and UI choices, and today we made a change to allow a larger number of the pages from the same site to appear for a given query. This happens for searches that indicate a strong user interest in a particular domain."
Search engines limit the number of search results from a domain to 2 or 3 pages that are usually grouped. The goal is to show diverse results and to prevent the websites from dominating the first page of the results. Showing too many results from the Apple's official site when searching for [apple ipod] is not a good thing because some people might want to read reviews, historical information from Wikipedia, news articles.
Sergey Brin said in an interview from 2004 that it's important to diversify search results:
"I agree that diversity of sources is a desirable goal, and in fact the results naturally tend to be diverse. We do some simple things to increase the diversity. If you check almost any topic, you will get diverging viewpoints. Everyone on any side of an issue will typically complain, though. Environmentalists will say,'Why aren't you showing our results first?' An industrial group will say, 'Why aren't you showing our results first?' They all want to be number one. We think it's good for us to encourage diverse viewpoints, and the search engine presents them. It happens naturally as a response to queries."