Caller ID Etiquette

Why does someone who receives a phone call with caller ID answer the phone by responding with a "hello?" when in fact they know who it is? Why pretend when the majority of people look at their caller ID before answering the phone? Most people SCREEN their calls and these days there should be no reason to pretend who don't know who is calling you.

Discuss?

Great minds discuss ideas;
Average minds discuss events;
Small minds discuss people.