MCV is stating that GT5's delay is due to the shoe-horning... inclusion of 3D and PS3 Move compatibility.The 3D aspect follows on from the recent
Killzone 3 announcement.
The unofficial MCV report states, "A source close to Sony has confirmed to MCV that the reason behind the more recent of
Gran Turismo 5’s delays is the implementation of both 3D and Move compatibility."
Source.