Hah, I deleted a whole extra paragraph of reply about how it "used to be phone books", and before that it was the operator at the local telephone exchange. How exactly would you go about telephoning the Smithsonian, then? You'd remember the number? Or you'd use some centralized facility?
No one remembers domain names either for a number of reasons: people use Google (aka, the telephone operator). If tomorrow all hostname were replaced by IP addresses, most people wouldn't even notice.
But... that's the point. Now Google is the operator. You still need the service somewhere in the chain! You can never obsolete the need to map the word "smithsonian" to some number or address - you can only move it around.
