Kill Bill did okay too. And even though Lara Croft sucked, it must have done well enough to warrant a sequel. Resident Evil - Extinction is still in the top 10 movies despite having been out for several weeks (and the fact they have made 3, count 'em, 3 of these movies is directly linked to its star).
I think the thing is there are simply fewer movies made with women as the lead which makes the chances of getting one as a top earner less. Tons and tons of guy as lead movies flop, but we don't refer to them as guy as lead movies, we refer to them simply as movies.
And yes, Chicago may have been a musical, but it did win best picture.
(oh and top grossing movie of all time, Titanic. It may have had two leads, but the film is actually narrated by the older version of the Kate Winslet character. It is her story really. Not saying the movie is any good . . . just pointing out another fact . . .)