Why would you have two sets of incompatible, yet expensive, lenses? One for stills and one for motion picture; two sets of filters; two sets of recording media, etc...what a waste!
That's certainly my thinking. I want the same lenses for both. And when a guy from a local ad agency who's shot a number of spots on RED with Cine lenses told me his last spot was shot with Nikons and then says the Nikon footage seemed sharper it ends the discussion for me. He didn't care what the name on the lens was, he looked at the footage. Like you should.