I was a little late to the party on this so I am going to rehash some stuff guiness has already gone over...
Midas wrote:the spirit of the GPL leans toward avoiding software lockout
Sort of. One of the arguments against permissive licenses (like BSD and MIT) is that this kind of thing happens all the time: a company picks up the code, adds some important features that ONLY work with their software and then releases it, effectively making their version the only version.
Although the FreeBSD people don't think this is a real issue, big companies including Microsoft and Apple use BSD code and give nothing back. Or -- in it's more nefarious form -- they take an open protocol, add some new features and then intentionally break the old connection method. It's anti-community and one of the major reasons the GPL was created was to push back against this tendency.
Maybe that won't happen here and of course we can't assume why UE's developers licensed their code as GPL, but I don't want to ignore their wishes either. These people put in time, effort, and energy to make a program a certain way and had very minor requirements for it's use and modification. I have benefited from their work so I want to respect their wishes. As such, I don't feel right using a program that uses GPL code in a closed format. Plus, how hard is it to release the code? Why would he close it? It just doesn't make sense to me. On a project made up of SO many different components from SO many different people, it just seems odd against what is clearly the result of so many people.
