That's the intention - (eg.
http://www.workswithu.com/2010/09/10/fluendo-dvd-player-for-... ). Like I said, it's early days though.
There are a significant number of Linux users who highly value the ability to see how the software they use works, and modify it as they see fit. Many of these users consider it a moral imperative that all software they run is open to inspection and modification. You won't sell anything to the people in this latter category - and you'll probably get a few angry emails, too.
On the other hand, there are also plenty of Linux users out there running closed-source NVidia drivers, Oracle databases and more.
