Richest South East Asians
It has always been a common complaint of anti-Chinese bigots throughout South East Asia about how the greedy Chinese accumulate their wealth at the expense of "locals" and "natives". Let me just make one point. The Chinese have been in South East Asia for centuries. The mere fact that their cultural motherland is elsewhere does not make them any less "South East Asian".
You think Thais just popped up on the banks of the Chao Phraya suddenly, one day long ago? Or that Malays simply appeared on the shores of the Melaka Straits? If you're going to get into a discussion about who is more "native" by virtue of the length that their ethnic group has been in the region, then perhaps the Negritos are perhaps the only real South East Asians. Everyone else? Well, sorry, you're just another immigrant.
So here is the theory behind why the Chinese seem to dominate so much of South East Asian business.
One. The Chinese got a head start. All newborn babies are born equally vulnerable and impressionable. So perhaps Chinese babies get a head start because more of them grew up amongst people in business, in an atmosphere of hard work and enterprise? After all, the China of the 13th, 14th and 15th centuries was one of the world's great military and commercial powers. The various kingdoms of South East Asia, for all their impressive development, had nothing on the scale of the great merchant classes of China's trading cities.
Two. South East Asia tended to attract the hard-working Chinese. One would presume that the person who bothers to make the tricky sea journey from the coast of southern China to the various nations of South East Asia in search of a new life is likely to possess the very attributes to help them succeed. If you were lazy and unambitious, why bother? You don't tend to see many lazy migrants - the sacrifices they have made give them the greatest incentive to succeed.
Three. The former European colonial masters found it most useful to use the Chinese as their agents. They got them to do the dirty work like collect the taxes. They did their business with the Chinese. They implicitly trusted the Chinese more because they knew they formed a minority and could thereby have no political aspirations of their own (think Indians in the African colonies of the British Empire or further back, the Jews of western Europe). The Dutch in the East Indies (now Indonesia) were masters of this strategy. After all, why empower the major ethnic groups like the Malays or Javanese by making them wealthy and influential? This was a lesson that former Indonesian dictator Suharto learnt very well. His most favored cronies were Chinese - there were no way men like Lim Sioe Liong or Bob Hasan could ever challenge him politically.
Accidents of history and a sense of being very much different from others - probably the main reasons why the Chinese have come to dominate so much of South East Asia's commerce.