SEA Games, in one aspect (at least?), is a joke. The host nations have become the overall winner since 1995, with the exception of Brunei in 1999 and Laos ten years later. The reasons are the host nations would hold sports which will be an advantage for them and they could afford to field the most number of athletes as well, since it would cost a lot of money for other countries to send their athletes for the game. Not to mention that a lot of sports involve subjective decisions (read: martial arts), which are largely biased towards the host nations, since the majority of referees will come from the host. Brunei and Laos became the exceptions precisely because they are small countries which could not afford holding too many sports for the event, and hence they could only hold essential or foundational sports (e.g., athletics and swimming). In that sense we could know the true champion of South East Asia from such SEA Games. And the champion of South East Asia is Thailand (duh, as if it is not obvious enough; and note that Thailand would consistently become the runner-up for those SEA Games held in larger countries). It is also consistent with Thailand’s performance in larger scale events, where host nation bias becomes less prominent, such as Asian Games and the Olympics. And Thailand consistently performed best among the South East Asian nations in these events (around fifteen years ago, I believe, replacing Indonesia — see again the above link, which showed how practically before that Indonesia ruled the South East Asia in term of sports). And that’s why Indonesia, the current host, will become the overall winner in the 2011 SEA Games.
(And that’s why, I believe, SEA Games is more like a bonding event to strengthen friendship among the South East Asian nations rather than a truly competitive event. It can’t be used for a barometer of sport development in SE Asia. Asian Games and the Olympics would provide a much better picture of that. Oh well, it is only a game anyway.)