During the Le Mans race, the demo labeled the track as premium. It was the first time the build of the track showed up. Until then, a 1080p upscaled version of Le Mans from GT4 was used in demos.
And they did have the GT4 tracks in HD, they used those tracks for the promos and intros of GT PSP, and for demos for GT HD, back in 2006. There´s pictures of people playing on Grand Canyon on IGN.
They looked very good.
Since we don´t have a logical explanation on why those tracks were left out, i hope they show up as DLC, togheter with Spa, whenever PD finishes that track. (going by the Jeux France video we know they are working on Spa).