git should really make it possible to use openssh/openssl keys for signing - so that I have one key both to push to github and sign my commits. I know that they can be converted from one form to another ... but its really inconvenient, especially on Windows, etc.

The GPG key is designed for a email based collaboration flow - that Linus uses. But most of us use Github or Bitbucket's UI to collaborate.

Github/Bitbucket should use this key in their UI as well - to show verified users.