> Is this not the job of the operating system or its supporting parts, to deal with audio from various sources
I think that's the point? In practice the OS (or its supporting parts) resample audio all the time. It's "under the hood" but the only way to actually avoid it would be to limit all audio files and playback systems to a single rate.
I don't understand then, why they need to deal with that when making a game, unless they are not satisfied with the way that the OS resamples under the hood.