Google search is a attempt at creating a mechanism to locate data that is not filed in any formal manner, like our library's or even businesses file cabinets. The data on the internet is just one big pile and finding anything, before search engines, was left to the advertizing companys to get the word out of what site did what.   Google's "page ranking" system is  proprietary and if anyone tells you that they know what it is, is a liar ( unless they are Google programmers ). The page ranking system probably uses some of the obvious parameters, traffic to site and relevance of search terms to sites main content. So by it's nature, one would think that the top pages are the authoritative source for information. But since it is somewhat of a popularity contest, at the least, the top pages almost never the authoritative source for information. While, you would think that the most popular sites are the ones that have to most complete and correct information. That just isn't true, as people try, and succeed in manipulating traffic to sites and plant certain words in an attempt to confuse the Google and others proprietary ranking systems, in order to win the popularity contest. And in Google's case, they have added fuel to the confusion by selling space on the page in the form of "ad words" advertising on the page, so that words alone trigger what is on the prime area of the page.