Here’s a post on SearchEngineWatch that does a good job of explaining one reason why it’s important to be continually adding content to your web site such as blog posts, white papers, press releases, etc
We’ve seen a shift in the way people search. Searchers are much more savvy today. They search on more complex phrases than in the past. In addition, more and more people are using personal search and local search etc.
Using site analytics we’ve been seeing people reaching client web sites using many more phrases than in the past (The Long Tail we’ve been talking about).
The importance of a few keyword phrases is diminishing. It’s become important to make sure you have the content on your web sites that will be returned for many phrases and variations of phrases. We expect this trend to continue.