Aamir has less movies in that list because he did less number of movies and not because because he was less of a star. Ishq which was released in 1997 had bigger opening than HDDCS which was released in 1999.
And that is also the case with most of these list. Aamir generally has less entries because he does less movie .... that doesn't he has less stardom.
well, even after being Aamir fan think Salman is bigger star, but I also think Aamir doesn't care about stardom(otherwise won't release Talaash 3 years after 3idiots), and any of khans can give biggest opeing in commercial genre, it's just that Salman is doing more masala movies, otherwise we can see in non masala genre Salman also doesn't give record breaking opening(e.g. Tubelight).