An important thing to realise is that success is not necessarily down to natural intelligence. It is certainly helpful, however. Success is determined by hard work and attitude. Even if you are inherently intelligent, if you do nothing about it and laze around, you will eventually be surpassed by those who may not be as intelligent but are more hardworking. Being a teenager myself, I commonly witness many of my peers act as if their dreams and ambitions will be handed to them on a silver platter.
Many Asian cultures revere hardworkers and it is admirable to be doing really well at school, even among your peers. Now I'm not saying that is not the case in the west, but I do get the impression that it is seen as "weird", "sad" and "uncool" to want to work hard in general and it is certainly the case in many places that those that excel far above their peers are mocked for doing so. The result is that sadly many people are afraid to work at their potential for fear of being mocked and seen as that "sad nerd". However, in many Asian cultures, competition and ambition are actively encouraged, so there is less of this stigma that doing really well at school is weird. Consequently, more people will work hard and so naturally more people will succeed.
From speaking to many adults, teenagers and children alike, I have realised that many people think that because they have not succeeded at something at their first go or find it difficult, it means that they can't do it at all and so they don't try. Practice is seriously underrated. Take a person who is musically gifted and has succeeded in this field. People will marvel and say things like "Gosh, I could never do that!" without realising or really appreciating the fact that to get to where they are, that person has put immense effort and hours upon hours of frustrating practice into it.
To be honest, I don't think that Asian people succeed more necessarily because they are more intelligent than white people, but rather that a greater proportion of them appreciate the value of hard work. I have no doubts that if more people in Western cultures realised this, they too would become just as successful.
Also, India and China have the largest populations of any countries in the world. Statistically, there are bound to be more extremely intelligent people who are Indian and/or Chinese. It's no massive surprise really.
There are many other factors I could mention but this post is already long enough.
One could actually write an essay on topics like this.