I didn't know that one, i'd of thought Khan v Maidana would of been Khan's highest viewing figure's in America after the build up and stories leading upto the fight
Malignaggi was a New Yorker with a little bit of a fanbase and he is a name because of his trash talk and some fights (Cotto and Hatton). Maidana wasn't a big name in America despite his style and Ortiz win.
Don't know the ratings but Oscar was a big name and ratings even 3 years back were a lot better. The HBO ratings have been deteriorating year by year. Here is an article that you might find interesting on HBO ratings: http://theboxingtruth.com/article.php?id=1931 Might be a lot to read but very interesting as to where boxing on HBO is headed