...Yes. When one does perform it should be for a live audience- so how do you know that people posting videos don't perform to live audiences? They may have uploaded the video for other people's opinions, and once they've improved, the go out and perform!
I do agree with you ont he matter that people are performing for their video camera and I really agree that is probably why the art of magic is dying. I know some of my friends never perform live and just perform for their cameras.
So on one hand PEOPLE PERFORM LIVE AND NOT FOR YOUR CAMERA!
On the other, 'Longman' you should realize that people may perform live and just not record it! Also, not everyone can afford a decent video camera
Unfortunately it is so that for the real live performers to make a video with no spectator, patter and no interaction and put it on web is like making a sandwich with nothing in it.
Personally i only perform on webcam for friends oversea, and i do that when we have voice-com enabled so we can interact.
How ever i can imaging myself showing an effect or two with some patter around and posting somewhere, but it would feel weird as it is missing some essential parts.
So in certain sense if u see those videos u do have legitimate reason to doubt if that person really do perform live, ofcourse some do but if some do not then it comes back to longman's point as it is a wrong direction in how this all internet thing is going.