You're saying it as if it's a bad thing.
Email is asynchronous. IM and SMS are disruptive.
And on IM versus SMS, the sender of a SMS usually doesn't know if the recipient received the message, while the default behavior of IM is to notify your contacts list if you're online.
These are different mediums people use for different kinds of communication / contacts.
But I don't expect Facebook to get this, especially considering their total disregard of the way people interact with one another. It's a wonder they are number #1, but I guess the alternatives sucked a lot more.