Creating something motivates most of the people on this planet, and without going into specifics, I would claim that Gateses and Jobses of this world are not all that rare as far as their abilities are concerned. Situation and, well, luck, are a big part of where life takes people. And having been provided for will discourage most from being as driven to "succeed" (in either financial or tech/scientific sense, two most common accepted ways to success on HN).
Which is to say: don't judge according to your standards of "success".
And raising kids is anything but science, unless you have such a large number of them that statistics applies (though even then, you'd probably be breaking a bunch of laws if you tried to be scientific :)).
As such, addiction to screens is usually, imo, an addiction to specific type of content, or rather interaction (or lack thereof) type.
It's actually quite interesting that you even consider Gates and Jobs having "great achievements" (other than business success, which is clear), yet condone screen addiction (which their core business were mostly about).
A quick search does not give me any study relating technical properties of screens to addiction-like effects: do you have any pointers? (Other than the common "LED-light-interferes with sleep patterns".)