Whatever the reasons, all contestants should be allowed to state what songs/act/music THEY intend to use. The only reason they should be asked to change is perhaps if more than 1 act was using the same music/song.
Andrew said he hadn't wanted to sing that song - Simon said "But you did...." Then Andrew said it was out of his hands. Easy to say he should have stuck to his guns, but less easy to do when faced with program producers etc etc etc all (probably) telling you what to do. I hope he gets another chance somewhere to prove himself.