Anchorhead said:

Call me completely untrusting of anything Officially Released By Lucas, but I wouldn't be remotely surprised if the damage & dirt were added for effect, or at least intentionally left for that same reason. It would certainly work perfectly for continuing the "I can't restore the 1977 version, it's too far gone" lies.
[/cynical]

Lucas could have released this footage on the home video market at any point from 1982 onwards.

I am just grateful to see it.

The dirt and scratches actually give it character.

Dirt ,scratches,weave,occasional soft focus(intentional or otherwise) are synonimous with film.

I remember watching the Two Towers at a theater in febuary 2003(2 months after it's release) and the print was full of scratches.

I am pretty sure when I saw SW and ESB back to back in 81' those prints were full of scratches too.

But quite frankly, who cares.

I would hazard a guess that the print you saw of SW in 77' was scratched up as well.