Simmon Phipps wrote a nice piece for his blog over on computerworlduk.com pointing out some great points about why closed source leads to less innovation.  One of the best ones is that closed source means that you always have to support it.  This keeps a lot of people from making the effort because they don’t want to the commitment.  Opening up the source code gives you the freedom to walk away or at least easily transfer management to another person.  Passing off the baton of leadership for your project so it can live on beyond you.  It’s a nice read with several nice points.