[kolinko]

The difference is that in this case the same colour will look different depending on how far away it is.

With regular colour correction things have a slightly different colour regardless of how far away they are from the camera, so the task is way simpler.

[pindab0ter]

To add to that, as I understand it Sea-Thru calculates what colour should be where based on depth information, even if the original colour information is 'lost'. This makes it more than a simple filter you apply.