Twitter replies question?

[JuicyJuice<3]

I'm confused about something. Only on certain tweets can I see other peoples replies to that tweet. For example...on one of @iansomerhalder 's tweets it took a while for the replies from other people to show up. And on one of @onedirection 's tweets they asked a queston...which implied that people needed to reply to that tweet so One Direction could see their answers. Only problem is...I couldnt see any replies?
What I'm saying is there are only certain tweets that I can see other peoples replies. And some tweets from famous people..I know people have replied, but I cant see them.
Is there something I need to do to see replies? Or has that famous person set it to where replies don't show publicly?
Help!?

[Matteo Ricci]

Its got to do with privacy. U wont be able to see a private account's reply.