Many manufacturers vetting process consists of testing that their products work with whatever OS X version is currently available to them.
Unfortunately, not every device fully conforms to Apple's specs. Windows works about the same way, but typically its included drivers are very bare-bones, so manufacturers supply their own to support advanced features. But the device still must conform to the specifications, otherwise the OS won't be able to access its functions or, in many cases, even be aware that it is an audio device. This is what makes 'plug & play' possible.
If a manufacturer doesn't supply a driver, the OS attempts to use the appropriate generic one in the IO Audio Family of IOKit drivers for all Core Audio functions.
A driver must still exist for the device to be usable with Core Audio & it must conform to Apple's specifications. It is not a driver or driver substitute but a set of protocols & abstractions. No offense intended, but you are a little mixed up about Core Audio.
