In a recap of those who passed during 2012, the NYT Sunday Magazine pointed out that the "Who shot JR?" episode was watched by 83 million US TV viewers.
The M*A*S*H finale had 106 million viewer and the Cheers finale had 93 million. By contrast, the Friends finale had 53 million and the Sopranos finale had 12 million viewers. Not sure how many the Jersey Shore group were able to pull in, but I'm guessing it didn't make the grade.