I don't know why, but it seems Celtic Woman fans whip themselves into a frenzy in a short period of time, as I've shown earlier. Now they're ardently denying that the show's latest creation "Songs from the Heart" isn't lip-synched. Look at the link for how they react. Note, the person isn't saying things like "Celtic Woman sucks" but is just saying "they don't sing live." (I also make a few postings here as Lunescent2007).
I've known that CW's shows have been lip-synched for some time now. When I first saw "A New Journey" on PBS in 2006, I didn't think they were, though my mother, who's unfamiliar with the group, said they were. I wasn't really convinced until I saw the "Christmas Celebration" DVD, where it sounds almost identical to a studio recording except a few little extras were added to make it seem live. After that, I've been convinced that they don't sing live, but that doesn't stop me from listening to them or watching their videos. It does bother me a bit that they don't show off their natural voices during concerts, but that's beside the point.
The point is, they do lip-synch. The voices sound identical to a studio recording and ultimately, that is what defines the matter. If you want to hear the girls' real voices (granted, the quality is bad, but this is probably as close to their real voices as we'll hear), check out the following links.
In the meantime, people don't need to leap all over each other just because someone says "oh, they don't sing live." All I can say is, good grief.