The AOW is a baseline, to keep you from being homeless or starving to death or having to beg for money.
For your last question: there are also people who are content with whatever welfare they get now and don't even try to work to better their lives. Even though everyone could do this it seems almost no one does.
1. AOW, the state pension
2. Private pension system regulated by pension law
3. Individual private pension
Slight nitpick on the AOW, you don't need to live in the Netherlands for at least 40 years. It's by rate, so if you lived 20 of the 40 working age years in the Netherlands you will receive 50% of the AOW (even if you leave the Netherlands).
In my own east european country, we have a stable Roma population (about 10%), of which cca 98% never work. They already rely completely on welfare system, to the point of making enough children to have large support payments (families with 10 kids are common, 15 is not unheard of, although kids are sometimes running around bare naked in the snow).
I can imagine quite a few countries would literally stop if given the option to just now work