It means they couldn't find the original film segment, or didn't want to pay to remaster it. When Vader speaks in the Holiday Special version, it cuts to the video screen Chewie's son is watching the cartoon on right before a commercial break.

EDIT: My "phantom memory" recalled Vader having lines before the commercial break. I checked against a copy of the HS, and it's clearly not the case. Sorry about that!

I still think this looks like it was pulled off of an analog broadcast tape though. The "countdowns" at the beginning and end as seen in the HS aren't there.