I disagree on q few things. You see the convention we are attending requires all skits to pre-record their audio and doesn't allow live mics during the skits. so everything is technically "lip-synced". Also it takes a good deal of work to edit a song.properly so that beats line up right and flows smoothly. It also takes a lot of work to take a song and create choreography that expresses the story being told. You also need to think about the work it takes to memorize the words and timing so that it looks smooth and like your actually singing. Also don't forget the work to build the props and costumes for the skit.
My first post is merely the bare bones basics to get the very general idea across. There is much more that will go into this then some may think.