This is by design, see this discussion. This policy is consistent over the network, and I doubt that they would change it for us. I guess that regular users with an account are supposed to know that the site has a blog. Also, there is a link in the footer navigation which doesn't disappear for users who are logged in.
The new Community Bulletin also shows blog posts when they are published, and specifies each link as "meta" or "blog". We moderators can manually create a link in the Community bulletin as long as the target is within the Stack Exchange network, and it stays there for the period of time we define. Blog links are inserted automatically when a new post is published, but I don't know how long it stays there. When there are no manually "pinned" links, the community bulletin is populated with random meta questions. I guess I could pin the last blog post for a longer time manually, but this creates the problem of a getting-used-to-effect: people may get used to seeing a "blog" type link on the community bulletin and not notice when it changes. If it is mostly populated with meta links but displays a blog link when there is a new post, users could be more likely to notice the change.
UPDATE: This answer is no longer correct. The link to the blog is never shown in the upper navigation bar any more. When there is a blog post, the community bulletin gets updated and shows the post. The link to the blog is still present on the bottom.