Blogs have come to be considered as highly effective, stand alone marketing tools. No self-respecting online marketer would dream of not having one. You can easily create awareness of your product (or affiliate products) by generating online reviews as your posts and receiving comments back from readers (customers). They are also a great start-up zone for the newbie where newbies can "wet their feet" without large start-up costs normally associated with static websites.
If you already have a traditional website, adding a blog can help enormously in getting good rankings with the search engines. Frequently edited and updated websites receive higher rankings in the search engines than those that have not been looked at by the owners for ages. Because of the dynamic nature of a blog, adding one to your site will give the appearance of constant positive site activity. New keywords can always be added to your posts. Don't forget to ad pictures and videos as well.
Most blog platforms allow for easy installation of other profit streams such as Adwords, Amazon, Clickbank and Ebay. I guess the keyword here is "easy". No programmers (costly) or maybe learning difficult html. Just click 'n' go!
Blogs can be pimped as you go along. They don't have to be "finished" at the start like the average website would need to be. Just start posting and fiddle with the design, settings and monetisation as you move forward.
It is not unusual these days for marketers to solely use blogs and to have abandoned traditional websites for ever. The only reason for a static website page would be for landing pages, sales pages or squeeze pages. These can easily be created and linked to from your blog and blog posts.
Everyone involved in Internet marketing really needs a blog. If you don't consider it necessary you may be cutting yourself off from one of the most effective and easy marketing tools in use today.