This always seems to be a topic of confusion amongst business owners wanting to start internet marketing for their business. For years every business just had a static site that never changed. The look, the content was always the same. These sites consulted of 5-10 pages and it was "what you see is what you get."
Times have now changed. Blogging platforms like WordPress or joomla are the best platforms to be build your website on. Period. They are so versatile it is ridiculous they can look like someone's personal blog or they can handle a heavy e commerce workload. Both WordPress and joomla based sites are ranking like crazy on the search engines. Probably the top 3 guys in terms of SEO gurus all you WordPress for their personal sites. That says a lot does not it?
The search engines love sites with lots of content, multimedia and lots of interaction. Think of the largest sites on the internet, the ones that always outrank you: Wikipedia, about.com, yahoo answers etc
These sites have hundreds of thousands of pages, if not millions. They get a lot of visitors interacting on their website by posting questions and comments about the content. They are a machine that is getting fed daily. The search engines know this so they park a spider on the site and gobble up the content and use it in the latest search results.
A blog is truly the best way to get your content out there as quickly as possible. For those of you that already have a static site do not worry. You can install a WordPress or joomla blog on to sub folder or sub domain. Like yoursite.com/blog.
That way the main core of the site will not be touched but you'll still be getting pages built onto the domain.