What's the purpose of having someone answer your phone?

Over at Ask a Manager a reader asks what to do about an HR person who called her first and now won't take/return the reader's calls. Ask a Manager gives an excellent (as usual) answer. It, however, brings me to this question: What is the purpose of having someone answer your phone if all they are going to do is send you to voice mail?

Yes, I know it's so that if the CEO calls, your receptionist can run and get you out of whatever important meeting you are in. Except, how often does that happen? Really? And if it happens a lot, then his admin can call your admin directly.

A couple of days ago I called a woman with whom I had been corresponding via e-mail. I needed an answer to a rather basic question about the German language lessons this school offered. What I got was the receptionist. She said the person I was looking for was not available, and would I like her voice mail? I said, "Oh, perhaps you can help me. I just have a question--"

"Oh, I'm just the receptionist," she said, cutting me off.

The funny thing is, in my experience this isn't unusual. So, why have someone answer your phone if they can't answer the most basic question? I've had bosses who insisted on the rule that "all calls be answered by a live person." This is good if the live person could help, but in practice, it just meant a live person saying, "Can I take a message?"

Now, I am not at all discounting the value of a good administrative assistant. I'm discounting the necessity of having a human, who can't really help you, answering the phones. Someone explain.