I Was There.........
I have come to this topic late, and I haven't waded through all the posts above, but I thought I'd put some of the latter comments into perspective.
I actually landed on the parallel runway minutes after the incident. Trust me, the weather was nowhere near as good as the weather mentioned above. We were flying an Airbus A320 and briefed to carry out an autoland due to the weather. On the radio, we heard the tower hassling aircraft to move up to the CAT I holding point. On very short finals the aircraft began to veer off the ILS centreline - ILS scales flashing, etc; we were - just - visual and the autopilot was disengaged and the aircraft landed manually. Sure enough, an aircraft was seen to be taxying on to the runway as we passed the threshold.
When on the ground I heard about what had happened to the SIA 777, I had my suspicions immediately that it was an autoland gone wrong due to lack of ILS protection.
FWIW!