well the 777 can probably fly an ILS beacon automatically but as far as i know, GPS is not approved by the FAA as a primary navigation device, certainly not for landings.
the "too used to ILS" is one theory floated on airliners.net. also possibly just fatigue, or maybe CRM (cockpit resource management) - supposedly korean air had this problem where junior officers just would not challenge the PIC when he/she made a mistake.
well, the NTSB is having a press conference right now and this does seem like loss of situational awareness on the part of the crew. 7 seconds before the impact someone on the flight deck called for increased power, 4 seconds before impact the stick shaker activated (stall) and 1.5 seconds before impact the call for a go-around was made and the throttles were pushed forward. engines were at idle until that moment which seems a little weird to me. given that it takes 10s of seconds to spool up one of those engines they generally trim the plane to allow the engines to be running at a few percent of thrust.
edit: also they were well below approach speed of 137kts.