singaporean, you are right to an extent. Having said that a lot of the jobs in singapore can be filled by singaporean, I know a lot of singaporean who just don't want the jobs that are available. Librarian, research scientists..... and also highly technical, highly specialized jobs in the industry.
My company is an MNC, and when we were looking for a researcher cum QC personnel for our lab it is impossible to get a qualified local (masters in science). Qualified and willing to work, sometimes shifts, on Jurong island.
Another instance, it's a little generalization but there are singaporeans who just quit the job because "they don't like it", or "don't like the boss". Quit just like that. For sensitive jobs, which require a lot of training, you don't want to recruit people like that. It's wasting an investment. I personally know two such people, not from my co but from others.
There are valid reasons why companies recruit foreigners. And it's not as you typify it, "above its own citizen's interest". You only have 2 million people here, and with the size of the industry here, like it or not you need supplemental talents. Made worse by attitudes of some!
You work in a big country, with bigger, much bigger pool talent. So the difference in treatment compared to sg.gov may be justified.
And last, I agree with you regarding the word "discrimination". It's not so much so. Or rather, if it is discrimination, it is practised everywhere. In the west, the asian feels somehow discriminated. In the neighboring country, chinese like me is blatantly discriminated, from certain jobs, from going into state universities etc. So yes, singapore is mild in that sense.
And I haven't yet known any good jobs that says openly "chinese only". Rather, it says usually "Singaporean or PRs only". Which is understandable.