It really isn't. Unless you have a card without a driver (exceedingly rare, though it's not uncommon to need a recent kernel to use recent hardware) ALSA pretty much Just Works. For complex features like streaming sound over the network you need PulseAudio, which due to its complexity takes more configuration and setup, but that's done out of the box on a fair number of distros. I don't know of any major software that requires OSS (though if I'm not mistaken it's still the preferred solution for BSD and therefore often available as an option), and only professional software uses JACK; users of JACK generally buy high-end hardware specifically for that purpose and know what they're doing.
So there are three major components for different purposes. Core audio support is the domain of ALSA itself and Linux does a good job with it. PulseAudio provides advanced capabilities on top of the more basic/hardware-oriented functionality in ALSA, and JACK provides low-latency audio for realtime applications that need it (not games, only really audio processing equipment). With large amounts of work the partial redundancy between these components could be removed, but it's really not a big issue; for desktop or professional use getting things to work right isn't too hard.
So there are three major components for different purposes. Core audio support is the domain of ALSA itself and Linux does a good job with it. PulseAudio provides advanced capabilities on top of the more basic/hardware-oriented functionality in ALSA, and JACK provides low-latency audio for realtime applications that need it (not games, only really audio processing equipment). With large amounts of work the partial redundancy between these components could be removed, but it's really not a big issue; for desktop or professional use getting things to work right isn't too hard.