This phenomena is obvious in singapore and I see the following reasons, but only for the chinese community.
1)Christians here are mostly english speaking. Generally the english speaking families here are in the high or middle income group. Civil servants (esp. the senior ones, since colonial time), and all professionals speak english. That is why christianity is regarded as western religion, angmoh ga.
2) on the other hand, chinese speaking only or those who quit schools before 0 level and turn to speaking dialects and english chinese form the majority of the population, in the middle or lower income group or the grass root level. Most of the 1 million buddhists, 200,000 taoists are among them and the others simply practise chinese traditional rituals. There are not many christian churches that cater to this group of ppl.
3) There are some very rich chinese speaking only singaporean, mostly in their own business but they are usually very strong buddhists or simply cannot accept christianity which to them is western culture and influence.
4) Christianity holds very strong position against gambling and unhealthy lifestyle, whereas followers of other religions believe that it is the good deeds they do that count. IMHO, those who gamble will never be rich.
Christians are still the minority among singaporen. Many churches are sending missionaries to thailand, india and other distant places, but how many churches, especially the english speaking ones, conduct ministry to reach the poor, chinese speaking populations in singapore?? well, these ppl usually have very strong traditional religious background and are difficult ppl, plus home ministry is definitely less noble sounding than overseas mission, leave it to the chinese churches, i suppose.