Although Webber is closer, he still changes a lot of the plot (even in the scenes that he retained from the novel) so in the end all he really is close in is the scenes but the the actually action taking place. Perhaps that's why he says it's "his" story, because on that level I can kinda of agree; it's so altered that it becomes an "original" story well fanfic, and it has some pretty catchy tunes in it!