

Unreal Tournament 2004 depends on SDL 1.3 when I recall correctly, and SDL is neither on Linux nor on any other OS a core system library.
Binary only programs are foreign to Linux, so yes you will get issues with integrating them. Linux works best when everyone plays by the same rules and for Linux that means sources available.
Linux in its core is highly modifiable, besides the Kernel (and nowadays maybe systemd), there is no core system that could be used to define a API against. Linux on a Home theater PC has a different system then Linux on a Server then Linux on a gaming PC then Linux on a smartphone.
You can boot the Kernel and a tiny shell as init and have a valid, but very limited, Linux system.
Linux has its own set of rules and his own way to do things and trying to force it to be something else can not and will not work.
The concept yes, the term for it (and the abbreviation) I am not sure.