Do i need to keep all the default WP templates files in a theme?

It really depends:

  • What is the intended purpose of the Theme? Is it a “special use” Theme, or merely designed for static Pages but not for blog posts?
  • What is the intended distribution method for the Theme?

If the Theme truly is a “special use” Theme, then you only need to include the template files relevant to the intended use. On the other hand, if you’ve merely designed a static-Page Theme, you really should take the 5 extra minutes required to ensure that the Theme also accommodates blog posts as well. The difference in underlying code between a static Page and a blog post is trivial.

If the Theme is intended to be submitted to the official Theme repository, and is not a “special use” case, then it will be required to support both static Pages and blog posts. The Theme Check Plugin is intended specifically to indicate issues for Themes to be submitted to the official repository, and that therefore must meet the Theme Review guidelines. If you’re going to distribute the Theme outside of the repository, then the Theme Check Plugin test results are merely for your own use/information.