Whichever way you cut it computers are rapidly approaching the point where fully autonomous commercial airliners are technologically viable. Indeed there are some very clever people working at this very moment on making fully autonomous air travel a reality.
However what computers lack is imagination, intuition and a sense of self preservation. How many times as a pilot have you had a 'gut feeling' about a situation where something just didn't sit right with you? I'm guessing a fair few times. Lets not forget that computers are only ever as good as the person who programs them.
Though the factor I think will ultimately keep the robot airliner at bay is the passengers. Would you want to put your life in the hands of a glorified calculator? I know I wouldn't.