Animating breathing is a pain to integrate into other animations, and even idle animations lack them sometimes.
If 'breathing' were treated the same way as 'blinking', then the depth and speed of breathing could be set to happen automatically, also.
Blinking and breathing are two things that characters will most likely be doing no matter what other motions are happening anyway, unless they are praying mantis or something. lol!
[EDIT] I just realized I posted this in the CC forum, rather than the iClone one. My apologies...