Also, from what I remember reading at the time, the HD master was edited by hand from the original negatives, unlike, say, The X-Files (which came to HD later), where much of the process to conform the HD scans to the SD master was automated.
We rented this movie and having watched it in the cinema last year, I thought it would disappoint in a High definition screen. It surely surprised me when it didn't look bad at all.
As for the MPAA thing, I also think the rating it got was ridiculously high. But, in Chile, it was rated Todo...