Under current law, software that is purchased can only be maintained by the copyright owner. Bugs and security holes can no legally be patched by any third party due to Digital Millennium Copyright Act (DMCA) restrictions. Leagally purchased software may become unusable due to Operating System or hardware changes, leaving the owner with no recourse.
I propose that the copyright be surrendered for any software that is 1) no longer publicly for sale or 2) is no longer supported by the copyright holder with patches or security updates.
The reasoning is simple: Copyright is to encourage creation of works for public consumption. Software that is no longer on the market is no longer serving the public good. Make it public domain and allow others to keep good programs alive.