Singapore is not nearly as isolated as NZ is. It's on a major ocean shipping lane and is just a bridge away from Malaysia. The problem isn't that NZ is reliant on imports (all countries are to a degree), it's that it is expensive to ship things there since it is out-of-the-way.

That being said, there probably is also a cultural element. I wouldn't really say it was a cultural shift. It's more that the relative stability and increasing globalization in the latter half of the 20th century gave Singaporeans the opportunity to realize their entrepreneurial ambitions.