I would imagine that after you had sung your song, then all the waiting around, sometimes for hours, to wait to see if they liked you or not, could start to strech your nerves a bit. So when you find out you have been accepted, it would be such a huge feeling of relief, that the 'boys' do hugs and the girls scream....although I don't like to hear girls screaming either.
And Dannii and Cheryl get paid for screaming.....If I was earning what they are earning on that programme....I think I would scream too!!
:-)