It doesn’t mean that you can create only publishing site within a publishing root site. To add other site templates, navigate to Site Actions --> Site Settings --> Modify All Site Settings. Click on “Page layouts and site templates” from “Look and Feel” section.
Add whatever site templates you are interested in to create sub-sites from publishing site. I have added a “Blog” template.
Now navigate to Site Actions --> Site Settings --> Create Site, notice that the newly added site template is available for you.
Hope this will be helpful to someone.