Comment 31 for bug 556593

OpenTTD-OpenSFX is Suggested because it is in Debian's non-free section and OpenTTD is in main. Debian's policy is to not allow Recommending packages from non-free/contrib in main. As such it is Suggested.

OpenTTD-OpenSFX is in non-free because it uses the Creative Commons Sampling Plus which is deemed non-free by Debian. That license has been "chosen" because all but one sample are from a database with samples under that license, the other is "public domain".

OpenMSX requires some sort of midi synthesizer, which is why OpenTTD suggests timidity and freepats. However, the suggests are not included automatically on installation, i.e. you need to install timidity to get the music working. Why that isn't a recommends I do not know, but I guess it has to do with the number of people that actually use the music instead of their own (external) music player.