Liz, I think the comprehensive point you`re making is good, and based on a combination of variables. 1) IF a small business has a Web site, 2) IF that Web site is well-made and functional, and 3) IF that site is mostly static, then a blog could probably help a lot.
On the other hand, a psychological question comes to mind. *Why* does the business owner have a static site, and no blog?
Maybe we could draw a correllation between small-business owners who
like to sell, promote, and market, and their having a successful blog?
Then there would be other small-business owners who don`t know how, or
don`t like to promote themselves, and so they have no blog.
If so, then the question would be what is causing the success of the
first type: the blog, or their personal interest in self-promotion,
sales, and marketing?