Kareena Kapoor is on a dream run and has seen the sort of box office success in the last 20 months or so that hardly any other actress has ever seen. Kareena in a near 2 year period has delivered four (Three Idiots, Bodyguard, Ra.One, Golmaal 3) of the top ten grossing films of all time.
There may have been a time when a certain artist may have had four top grossing films in the top ten but those releases were not in a less than two year period.
The only other time when an actress achieved a similar feat was Hema Malini in the 75-76 period when she had three films (Sholay, Dus Numbri, Sanyasi) amongst the top ten grossing films of all time and a Pratigya just outside the top ten. Sholay and Dus Numbri were amongst top five.
Hema Malini is the most successful actress at the box office and probably the only actress in history to have box office clout in an industry that always goes by the male lead. Since Hema Malini, there have been many top actresses like Rekha, Sridevi, Madhuri Dixit, Karisma Kapoor, Kajol and Rani Mukherjee but it is Kareena Kapoor in the last two years who dominates as far as the volume of high grossing films go.
Katrina Kaif also had a huge run in 2007-2008 with Partner, Welcome, Race and Singh is Kinng but all these films were amongst the top 15 at that time but with nett numbers not actual grosses as entertainment tax started to come down heavily from 2003 onwards. But with her line up in next 18 months or so it could happen again with gross numbers.
It is true that the Kareena Kapoor starrers are helmed by the reigning Khan's but that will always be the case as its a male lead dominated industry and even the Hema Malini starrers featured megastars like Dharmendra and Manoj Kumar who where as big or even bigger in that era than the Khan's are now.
When actresses have huge box office success be it Kareena, Katrina or even Hema Malini, there are many variables to it but to have four films in the top ten grossing films like Kareena Kapoor has at the moment is still historic because it has hardly happened before as it tough to have all your major films to work in a big way as one or two are always likely to fail you.