Showing live gymnastics is really hard b/c you have 4 rotations going on simultaneously, with 2 teams at each station, and it's absolutely impossible to show everything that's going on at once. Showing taped gymnastics is much, much easier. Plus- with a live event you need to focus on the pre-set stories and it becomes very hard to change in the middle. In men's gymnastics it was the dominant Chinese team, the surging rookie Americans, and the middling Japanese. For women the main story was the US and China, as well as that 35 year old German (who's actually Russian) who won a medal on the vault. The general population in the US wants to watch the best teams and the Americans (and not necessarily in that order), and in this case they were one and the same.
I don't think NBC was perfect with their general coverage, although almost all of the announcers should be shot, but they certainly did an above average job with the material they got.