Where is that site which listed the reasons for wanting F/OSS, pointing out why one would care more about the license for the software on a laptop than a microwave?
I think its pretty relevant here.
F/OSS has far greater practical relevance for tools than for games.
If some part of a game was made into a general library, for some reason, then the importance of the license for that would instantly increase.
And what if the save data is some proprietary data? The worse that can happen is that you lose it, and its not important (as opposed to work related material)
I don't think RMS would requite artists to hand out the PSD-files with all the layers intact (because otherwise you can't change it as easily), or otherwise refuse to look at it.
Nor refuse to sit in a car that was designed using proprietary CAD-software.
Just like a car or a painting, games are an end-product. It just happens to be digital.
* B.t.w, This might actually also push for better open source GPU drivers