Here's a good description from Tesla itself of Autopilot:
Dual Motor Model S and Autopilot | Blog | Tesla Motors
Lane change is initiated by the driver (tapping the turn signal) and not automatically by the car. This eliminates the need for long distance rear sensors. The driver will still need to check the rear view mirrors for oncoming high speed traffic before initiating a lane change... much safer (and easier technically).
Agree. I think people misinterpreted what is being offered. Tesla never said the car would decide when to change lanes or whether it was safe to change lanes (though BSI will let you know when it's definitely not safe to change lanes). It just provides a mechanism for changing lanes during autopilot mode (which is basically adaptive cruise control and lane keeping) without having to put your hands back on the steering wheel. The driver is still the one making the decisions of when and if it's safe.