I think it's better to have them (see http://docs.python.org/2/distutils/sourcedist.html#specifying-the-files-to-distribute , tests are intended to be included). Regardless though, it seems a mistake to be including the development requirements if we're not including tests.

https://github.com/saltstack/salt/blob/develop/MANIFEST.in
https://github.com/django/django/blob/master/MANIFEST.in