Cowboy Bebop...Firefly...could they possibly be related?

Are all groups of cowboy-designated thieves on a space ship - featuring an innocent girl who's good with machinery, a tart with a heart, a hulk of grumpy stupid manflesh and a hot lead who looks good in tight pants - necessarily related? Is everything that echoes linked, or am I linking them just because I'm looking for connections to things I know already, forming a comprehensible map of a crazy world?

See: The Regeneration of the Cool.

Recyling my own ideas is ok when it's a matter of perennial truth. Yup.