Not to make this political DonM, but it is a common SciFi theme that the "best and brightest" leave Earth for the stars and the "Meek and Boring" stay behind. There are many examples in literature of a conservate Earth with a more vibrant, expansionist culture in the stars around them.
This is an extreme example but still within the spirit of our SciFi roots.
But, you also only really have 2 kinds of Terran natives in an interstellar future:
1. Terra Dominates (Terran Empire, Traveller's ROM etc)
2. Terra is Inconsiquential (not there, conquered, a small fish in a big pond, run by fruitloops)
Yeah, I pretty much agree. American sci-fi, in particular, seems fond of the frontier myth (which I actually don't think is a myth, but I digress).
I should stress that the founders of the Commonwealth were *survivors*, not the "best and brightest".
But they were ideally suited (however accidentally) for the forming of a successful interstellar state. They came from comparatively free, egalitarian and open cultures (by 21st century standards). Their pre-war choice to live in space or colonize other planets meant that they were psychologically better suited for cutting all ties with Earth and colonizing Haven.
Their cultural assumptions -- free speech, free markets, individual rights, religious freedom, separation of church and state, consensual governance, gender equity, etc. -- were ideally suited to forming a successful new society. TL10 CNC machine tools and assemblers, templates for a huge variety of machine parts, advanced nuclear power plants (cannibalized from starships) that deliver effectively limitless amounts of energy helped a lot too. Oh, and electronic versions of virtually all fiction and nonfiction works in human history didn't hurt. Then there's TL10 medical technology, which allowed a tremendous boost in fertility rates over early 21st century Earth. SS Conestoga and SS Botany Bay, which were colonization ships, had frozen sperm and ova of a wide variety of Earth animals (and humans).
And of course, Haven, Matilda, Kamakura and Lincoln are very fertile worlds with excellent climates and an environment nearly ideal for human beings and other Terran lifeforms. They also enjoyed no small amount of luck, in having no local enemies and being far away from the strife on Terra. And of course, in having their worst enemies nearly destroy themselves in internecine wars. Finally, while the record is sparse, it does appear that Admiral Lee, President Thorpe and many of the Framers of the Commonwealth Charter were gifted people.
In other words, the Commonwealth was about as lucky at its inception as, say, the United States...
