The CommunityServer Staff (aka Scott) has announced the decision to remove MetaBlog API from the main CS download and make it a separate download (with some improvements).
If you plan to install the new CommunityServer to host your blog engine, remember that if you want to post on your blog via external client tools (such as BlogJet, w.Bloggar, IMHO or similar) now you've to download the zip provided on the post above and install it.