Ultimately, I see a hub as more like an article you'd find in a print magazine or in a newspaper. Even the opinion writing, which is what I mostly write, is more fact based, and contains more information such as you'd find in a news-based article or in a column than say, a blog. I write blogs too. But blogs are quick, off the cuff thougts. Hubs are better in content, better in quality, and slightly longer in nature.
To illustrate my point here is a blog at my blogsite, http://www.springboardblog.blogspot.com/2010/02/if...
Essentially the same as my hub at http://hubpages.com/business/some-companies-firing... but the Hub is obviously more detail and fact oriented, whereas the blog is more concise and direct, and more opinion based even though much opinion is enfused into the Hub as well.
Hope that helps.