Yes indeed the first WipEout had day for Venom and evening/night for Rapier, but guess what: that means there were two sets of textures for each track. It most certainly doesn't calculate the lighting for day or for night all the time (That would be horrible for the loading :O)
If anything like this is implemented in WipEout HD or future ones, it would be the same thing: darker textures for the night, some reworked prebuilt lighting and that's it (Well it's a lot of work, but after that work that's it ). But this doubles the size for each track as I said, because you have two textures slightly similar but one is darker than the other.
I guess it has not been brought back because of the amount of extra work needed to pull it off.