You do realize they are comparing Leno's RERUNS vs. new episodes of Conan? Reruns rarely do as well in the ratings as new episodes and it would have been bigger news if the reruns did better ratings than new episodes. Not only that, but the reruns aired later than normal due to tennis coverage on NBC. What is interesting is that RERUNS of Leno still beat NEW episodes of Letterman (0.9 compared to 0.8 ). I would also like to point out that the article you posted only talked about one specific demographic (adults 18-49) rather than overall ratings.
Leno is also doing something that Conan rarely ever did, beat Letterman. Leno has beat Letterman every week since returning in March. Pretty much the only time Conan did that was after it became public that Conan was quitting NBC. Conan started off strong, but by September his ratings had really dropped.