Here's why. Web sites are great, but they also simply provide information. There isn't much interaction possible with visitors. (This 'generation' of Internet usage is called Web 1.0.) For Web 2.0, however, interaction with visitors is critical. A blog is a great way to facilitate this interaction with your customers and prospects, as people can post comments or questions, which you can respond to.
Blogs also have these other advantages:
1. They can be updated quickly and easily, which make them ideal for specials, announcements, etc.
2. Key "search engine optimization" terms can be used, assisting with your Google search engine ranking.
Take some time to consider creating a blog for your business. Yes, it will take time to build it, and there will be a learning curve. But once you have it established, a blog can become an essential part of your marketing program.