I recommend reading Jared Diamond's "Guns, Germs, and Steel."
He comes to the conclusion that "Necessity is the mother of invention" is bunk by broad historical analysis.
In truth "Invention is the mother of necessity."

The larger our cultural/technological base and the number of minds at work, the greater the number of inventions. Usually the existing technology is around before the need arises (whether through public need or market demand).

The examples given are exceptions to the rule.
That's not to say that they don't make an excellent point. Sometimes we do put minds to work best by concentrating on a goal as a society. But I think it's mostly limited to public goods. But I guess the internet is an example of how an intended public good can become a lucrative private good...
Interesting because that's the opposite of how things usually go.

I suppose the lesson is that there is no golden rule for how innovation comes about.

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"Man lives in the sunlit world of that which he believes to be reality. But unseen by most is an underworld, a place that is just as real... but not as brightly lit... A DARK SIDE!"
-opening from Tales From the Darkside