GUI and autocompletion aren't mutually exclusive. In fact I think they compliment each other well. See: your browser's address bar, google's search form, etc. If you're doing anything non-trivial with a GUI, chances are you're using a keyboard of some sort at the same time, and those interactions often benefit from autocompletion.
The reason we're still using keyboards, which are basically late-19th century technology, is because we've yet to figure out a faster and more precise method of getting words out of a human brain and into a machine. You could quibble over qwerty vs dvorak or chorded stenotype keyboards, but all share the premise of speaking using your fingers.
(Voice recognition isn't there yet and probably never will be if human-to-human interactions are anything to go by (it's common for humans to use text to communicate with each other when they need to be precise, even when both share a common spoken language.))
The reason we're still using keyboards, which are basically late-19th century technology, is because we've yet to figure out a faster and more precise method of getting words out of a human brain and into a machine. You could quibble over qwerty vs dvorak or chorded stenotype keyboards, but all share the premise of speaking using your fingers.
(Voice recognition isn't there yet and probably never will be if human-to-human interactions are anything to go by (it's common for humans to use text to communicate with each other when they need to be precise, even when both share a common spoken language.))