It's a secret message!
"Paul is dead."
OH NOES.
Seriously, though, that is an interesting find. I actually like the Hayley-backing vocals a bit more than the lead sometimes. And example of this is, if you went to The Final RIOT! tour, chances are you hear her do some backing, while the crowd sang the lead to the beginning of Crushx3.
Exhibit A: http://www.youtube.com/watch?v=PAF1XO60sgo