well, this clapping-kind-of-thing is definitely something that has just come up since about 15 or 20 years and was, I can only speak for europe, totally unknown before. I guess this might again be a "custom" inspired by romantic Hollywood movies, as well as the kiss in front of the altar!
I never attended a catholic wedding where somebody would have clapped! Everyone is happy and cheerful, but a churchservice is not an entertaining show. Old-fashioned? May be... But I really feel that our old traditions and customs are being overshadowed by the american entertainment industry and culture which I often find of a foreign conception having a disturbing effect especially in historic documentaries, which should aim to trace back an original period or event as detailed and accurate as much and just get trapped by our modern way of thinking and doing things, which I think is unscientific.