I think blogs and facebook pages really serve 2 different purposes so it's nice to have both. I've hooked my facebook page to my blog so whenever I do a new post, it also shows up on my FB fan page. I think it's harder to get fans to your page tho, than it is to get readers for your blog, at least that's been my experience.
Your blog is out there for anyone to read and if you seo it, many will find you through web searches. FB is a closed system where only other users will see your page too. SEO doesn't really help you on FB.