Blogging tools have several characteristics that make them a CMS. And they are very important, because arguably as much content is being managed in weblogs as in all the content in more standard CM systems.

• Blogging tools separate content from presentation (layout). This is a major time saver when the blog needs to be redesigned. Change the template, and hundreds of pages change together.
• They often separate the development staging server from the delivery server.
• They use templates and feed content objects into the templates. However, they do not have a WYSIWYG template editor.
• They use RSS aggregation of feeds and syndication of stories. See Trackback and Pingback.
• They have WYSIWYG editors.
• They can have multiple authors (team blogs), but rarely have any workflow.
• There has been some effort toward a BlogML to facilitate semantic markup with XML, but that has largely failed.
• There is a Blogger API that allows independent client tools to post to various blogs.
• As with CMS, you can buy blogging software and run it on your own web server (notably Manila from Userland and Moveable Type), but few blogging tools are open source, and most are provided as ASP hosting services. The great majority of individuals blogging are doing it on "free" hosts like Blogger's Blogspot.com.