The blog module is part of Drupal core, and existed before CCK and Views.  Drupal core doesn't technically know about - or use - CCK and Views.  It just sits there happily in its CCK/Views oblivion, making content types and listings available.
Rather than Views support, it contains a hard-coded link to a list of say, "tara's blog".  And it adds various links throughout the site to blog posts, etc.
This is quite handy if you don't have CCK and/or Views installed, and still useful if you *do* have those installed, but are happy to take what the blog module gives you for listings and links.
If the blog module didn't exist in the first place, one might think "hey, why don't I just create a 'blog' content type, and then add a view that lists all the blog entries?". You can totally do things this way, which is a little more time consuming than the out-of-the-box functionality - but way more flexible.
Hope that helps!