This is a bit of a bait and switch, because all of the options the author lists are solving problems (even if just improving upon existing solutions, you are still solving sub-problems of existing solutions). Instagram readily solved a problem: photo editing / stylizing had been difficult and/or expensive prior (yes, I hate their filters as much as the next guy, but most people find some value in it). It may have not been the first app to do it, but it still solved a problem.
<i>Because most of essential problems are already solved, you can only find solutions for unsolved small problems that interests only small group of people.</i><p>I disagree. Some huge problems remain unsolved because they are big beasts to tackle. Education, for example, is ripe for disruption, and while there have been some advances (Khan Academy, Edx), we have a long way to go before you can get a respected degree online.
For the last paragraph, I should add that Yandex was founded before Google. <a href="http://en.wikipedia.org/wiki/Yandex" rel="nofollow">http://en.wikipedia.org/wiki/Yandex</a> It is not an application of a global idea.