Over the last few years we’ve seen a sea of change in the way search engines (primarily Google) rank websites. Until recently, the most effective technique for ranking on page one for any given term was simple brute force: use your primary keyword regularly throughout your content, and build as many links as possible back to your site using that keyword as the anchor text.
As you’d expect, this technique was open to all sorts of manipulation. Those with enough money could simply buy links, and while the algorithms used by the search engines weren’t quite simple enough to be fooled every time, it was common to see poor quality sites at the top of the SERPS (search engine result pages).