I've only watched a small portion of the "Celtic Women" show. I just found it to be too big of a production for my personal taste. I've no doubt, others will enjoy it immensely but as to your question re Lip Synching... Whether they are or are not lip synching on this particular show, I don't know but when it happens, isn't the performer admitting that he/she can't actually do what you're paying them for? That, to me is a rip off?
GUEST,Shimrod: Yes. That's what we call miming now. Don't know why. I suppose they're giving credit to the technicians rather than the artists. Hey! Makes sense when you think of it.