I think the big question here is of Intellectual Property. Taking Microsoft as an example only (and not targeting them specifically), the belief is that MS Word should not be redistributed by anyone other than Microsoft Licencees. The reasoning being that they have put a lot of intellectual work into it and they should be compensated for it. That is true. People should be compensated for their ideas - if those ideas are revolutionary. The ideas in Word, and almost all commercial software are by no means revolutionary.
When DOOM first came out, it was revolutionary. The amazing graphics on a 386 really `kicked ass', as the expression goes. They had every right to keep the source closed for as long as they did. ID Software realised something that most other developers don't. Soon enough, other developers figured out how to write games like DOOM, and then Carmac and Abrash wrote so many books. ID decided to open source doom (or was it Quake) at that time. I think they first started by giving away level editors free.
All game companies give away level/map editors today, but how many have opened their source?
NOTE: I use open source and not free software here.
Philip