This can be a chicken and egg thing. Has any one thought that the pinoys were not warm and friendly because of the Sinkies' initial response to them? That we Sinkies didn't receive them warm and friendly first because they were here to take our jobs and as a result, the pinoys replied back in kind. So the pinoys see sinkies as unfriendly and cold, so they don`t even bother to ask before taking a seat in the food court etc.
If you meet pinoy overseas, they seems to be warm and friendly but then that could be because the pinoy is in a foreign country, he needs to make friends with other foreign nationalities such as sinkie in a foreign country.
My last trip to Pinoy land was many years ago, I don't recall if the pinoys were friendly in their own country to sinkie or foreigners. I think the pinoys were not warm and friendly in their own country just like HongKies were not warm and friendly in Hong Kong due to the rat race.
No matter what, the pinoy being guests in Singapore still should be warm and friendly to the locals, their behavior now can be considered as a rude guest.