Sure, you could do this on another platform as well. On Linux, for example, if you have a way to have the distribution provide packages for the runtime libraries, you would not need to package them. But, the compiler used to build that must be the exact same one (ignoring the fact that you may be able to get away with some divergence in reality). Failure to do so means that your program may or may not work with the runtime on the system since the compiler makes no guarantees about the ABI on non-Darwin targets currently.
What it comes down to - Apple has made the necessary engineering investment to provide a guarantee over the language ABI and governs the releases of their OSes to ensure that the runtime conforms or provides a mechanism for backwards compatibility. If someone else wishes to put forth that effort, nothing prevents other platforms from having a guaranteed "stable" ABI. (Just to give a rough guide for effort required: to this day, Microsoft does not provide a stable C++ ABI, nor does any other platform, except perhaps Apple?) This is simply a contract, and there are obligations towards fulfilling that contract that Apple has stated that they will assume.