SilverWook said:

Wow! I never saw the ghost before! With what Empire of Dreams revealed about the editing process, it's possible that was the only shot of the homestead at that angle they could use.

I too never noticed that before. What would make Luke appear ghost-like? Judging by Luke's position that was probably taken right after he viewed the sunset.

As for why nothing has been changed for the Blu-Rays, it's probably just general Lucas laziness, thinking the product will sell in any form.