that is misleading Coreaudio = ALSA. and Jack = ASIO,rewire,Soundflower. if jack equaled Coreaudio, it would handle the all of the audio hardware drivers, but it doesn't. instead it runs on top of alsa..
Jack is the equivalent of ASIO+Rewire+coreaudio+Soundflower. It is sample accurate, synchronous and suitable for professional use. There is no hidden sample rate conversion or bit depth reduction. This is what people who are recording music professionally want.
I hope that clears things up a little.