Mavericks said:

In short: DVD and BD versions of OT didn't hide all dubious artifacts of the special effects of the era. It most affected objects (ships) in motion.

This is true and it's not because Lucas' team lacked sufficiently-advanced technology or was on a limited budget.

It's because they did a rushed half-assed job and only "improved" the original FX that they considered to be most noticeable.

Lucas was (surprisingly) happy enough with this shoddy work to call it his "original vision" or whatever...

Yuck.