As many before me already cleared it out, Beyonce can actually sing amazingly live 90% of the time. That's why she gets a pass when she's lip synching.
Comparing apples to oranges. A great vocalist can get a pass for lipsynching cause everybody know damn well of what he/she is capable of. This Beyoncé's incident in particular is comprehensible af. What is not forgivable is to keep on with the lipsynch without good reasons to do it, and if your pre-recorded vocals are not that good on top of it = mess all around.
Girl... it's different to lipsync here and there when the situation absolutely demands it and lipsync every single time for the past 10 years to the point people don't even know your voice anymore.
Also, if you're going to lipsync - at least go to the studio and prerecord some "live" vocals to give people the illusion you're singing live. Pop artists are in the business of selling illusions and fantasies. By lipsyncing to the CD track you're breaking the immersion between the artist and the audience. It's cheap.
