Chris-
I posted a link to a blog under "resources" that addresses the research having to do with timing accuracy and processing speed:
www.ticktockbraintalk.com

You are right that the basic principles are the same as dance. But a lot of people are unable to keep time with the music and can't move with the beat or learn a routine. IM (and any other timing, rhythm training) addresses the skill at a very basic neurological level. I had an adult I treated with IM be *able* to dance after completing IM. He never enjoyed dancing before because he couldn't keep the beat or get the timing - always stepping on his partner's toes!