If Apple takes it upon themselves to write/test drivers VS relying only on the manufactures to do it, then you are sure that since apple has a stake in it, they will test it well. This is a consequence of controlling what hardware goes into your computer. If you want to plug your soundcard into a mac, better get in touch with apple. Since they know about all the sound drivers, video drivers, etc, they can group where necessary. Being *nix based also gives benefits of having open source drivers.
In any case how many different drivers are out there for Windows Sound? How many are out there for Linux? Bash ALSA or OSS all you want, but they support a ton of hardware, port that sort of support to windows or mac and you got yourself ONE driver heavily tested by freaken' everyone which makes debugging easier with a central point of service.