1. You can write so much more and explain what you mean in more detail, rather than having to make a quick update that may be misunderstood.
2. You don't have to use your full name (or even your real name).
3. You can limit your audience more. If you want to blog without all of your acquaintances finding it and reading it, it's easier to do so - just don't tell them or advertise it on Facebook.
4. You get to 'meet' new people. Facebook tends to be about connecting more with people you already know.
5. There are more customisation options. You can 'personalise' your blog more than you can your Facebook page.
If you're a blogger who's also a Facebooker, what ways do you think blogging is BETTER than Facebook.