Its manipulated greatly, you will se on Saturday that 3 of them will get lower brow celebs and one of them (who will go onto win) will have some superstar.
Look at last year, Olly had an intoxicated Robbie WIllimas who forgot his words, Stacey had Michael Buble and Joe had George Michael...
It happens every year, i genuinley belive that the judges chat before hadn and are told who to keep in on the the sing off.
Its more obviousl this year than in the past.
There are rumours that Matt is singing with Christina Aguleira (sp?) and Rebbecca with Amy Winehouse.. not sure about the others Cher will proably have Jay Z if they can get him and wand erection will have an amazing boyband, maybe TT again?