Hmm, seeing that Morning Musume obviously lip-synch's some of their lives, I don't think there's a law in Japan against synching.

I think Ayumi has lip-synched before, although the incidents are few and far between. There was one performance of SEASONS that I'm almost positive was synched, but it wasn't in front of an audience and there was no band either. Also, there was one mini-concert where the vocal quality sounded different for the 2nd half of her set so I think maybe there was a background track ready in case she started losing her voice. In any case, lip synching doesn't bother me too much as long as it's entertaining. Plus, when there are high energy dance routines, it's easy to get winded.