One of the things that can help distinguish your website from your competitors is how often you update your content. We all know this, but yet some of us still find it difficult to make changes. This might be the rationale behind Google putting stock into how recently and how frequently a site is updated. Google prides itself on giving searchers the most relevant information available, which a lot of times will translate into the freshest information available. Google will rank sites that administrators care enough to make changes to higher than their stale counterparts.
Now obviously, Google isn't ranking sites soley based on frequency of updates, however it is one piece of the overall equation. In my opinion, it is the easiest piece of the overall SEO equation to put into action. Invest in a good content management system and swap out a picture or two every once in a while, blog about news worthy events, add a landing page that correlates to a new ad campaign. Make your website work for you. It's easy with the right tool.