Go here: http://greg.org/archive/2009/01/19/wait_whered_stars_wars_a_capella_guy_go.html
He said it better than I.
It's a parody--the copyright laws as such don't apply. Plus, while Warner owns distribution/publishing rights (including songs put with images) of the songs as well as the recordings of the Star Wars theme, that song is not in the video; I can't seem to track down the publishing rights-holder for the songs that actually were parodied.
