Replenishing the dying stock of good genes
This may not have been spoken as an official policy statement, but this is what I think could be the key reason. As our stock of good genes are dying away quickly, and we are unable to find the same quality of equally good genes, despite paying so much, it is necessary to import from abroad. In a generation or two, we will have all the great genes we need, from sweepers, cleaners, bus drivers to doctors and researchers. Then we can claim to the world that we have the best sweepers, cleaners etc or best workers of the world. And this could be the reason to pay them world class salaries as well. At the rate it is going, the workers, or those at the bottom 20% could be getting $3k-$5k pm or a household income of $10k. And they will be considered the lower income group. The average Singaporeans, with world class genes, will be getting $20k-$30k pm. This will be the future for a city of excellence in the future. Dunno what will be the cost of living then.