First I have to say that I do not want to offend or hurt anyone, but I just have to express my opinion. If I have offended you, or hurt you nonetheless, then I am very sorry.
Lately I've been using twitter a lot. I like to keep track of what my friends are doing (not that a lot of my friends are on twitter, but whatever) and to follow some persons I like or admire. What I like about twitter is that you can “talk” with people you normally can't, like famous people or people from the other side of the world. The only problem about that is that you get from these fan girls who tweet non stop to their idol and get disappointed when they don't get an answer.
Just place yourself in the shoe of a famous person, would you like to waste hours and hours on replying to every single tweet you get? I wouldn't. It's not because I wouldn't like my fans but more because it takes so much time and so much effort.
Trudi Canavan for example, doesn't even reply on her fanmail because she just doesn't have the time to do it. She just reads it.
I think it is very selfish to demand an answer from someone, or be disappointed when you don't get an answer. Or people who are disappointed that they weren't online when there idol was. To be honest, I have the feeling you are beginning to become a stalker then.