Housing is basically a govt supported investment program in Singapore. Not that different than most Western countries, just different mechanism.
HDB certainly helps to lower the barrier to entry in home ownership. But I don't think most forms of HDB purchases are investment-orientated. ROI for second-hand HDB is not high and buying a good first-hand one is like winning a lucky draw.
I would say HDB is more of the gov's mean to stabilize the housing market and it functions as more like the backbone of the economy. (Or you end up with runaway prices like in Hong Kong.)
HDBs are similar to property in most countries. It’s bought primary as a place to live but also as a store of value. The govt will buy out your HDB for cash in order to fund your CPF. The govt also constrains the supply of HDBs which pushes up values.
But you are right about the lucky draw. Someone people win BTO lottery and make out like bandits with new developments in mature estates.
Also, rent here is so expensive that most Singaporeans still stay with their parents even in their late 20s~30s. (Most people renting a room or apartment are none-Singaporeans (30% of the population).) So buying a house makes perfect economical sense if you are married and can somehow cover the down payment.
I wonder if this is becoming a trend across all first-world countries, as the world gets less predictable and people get more risk-adverse. Esp when rents are driven up by none-citizens so it becomes economical to buy instead of rent.