Yes, the original 1977 release contained C-3PO's line... well at least some of the prints did. I think that most people don't know or realize that in 1977 Star Wars was released with no less than 3 different sound mixes: 70mm 6-track, 35mm Dolby Stereo, and 35mm Mono. 3PO's line was definitely in the mono mix; this is a fact and I do have a bootleg tape from '77 to back this up. I am now uncertain if the line was in the Dolby Stereo mix, and I personally think it was absent from the 70mm 6-track mix. So depending on which version you saw at the theater, you may or may not have heard this line.

As you mentioned, the '89 widescreen LD has the line. It was the first, and remains the only, laserdisc of the original film to contain this line. All VHS releases between 1984 and 1992 also contain the line. The THX mix, or course, left it out.