Is Google unique in having numbers like this? Well certainly not completely, probably not even a little. AAPL, NVDA, and a few other companies have all smashed through the $1,000 billion mark for post-IPO investors while very likely having only done at most tens-of-billions for the pre-IPO investors.
So I think the suggestion that the early investors "reap the vast majority of the reward." is precisely wrong, even overwhelmingly wrong.

Interesting that you pick three of the, perhaps the most successful companies in recent history to demonstrate your point. I wouldn’t know how to do it, but I suspect if I could find a normalized way to do the calculation for all companies which have gone public the math would point in a quite different direction.

I once inherited a station with a ratings problem (I didn’t want to go, but that’s another story), and the CEO decided that to “help” he would get a consultant for us. Who came to town, and in our first (and only) meeting told us this would be pretty easy, all we had to do was “find another Oprah.” I should have fired him on the spot, but because he was a download from above I bit my lip and kept my mouth shut.

We never did find another Oprah. Nobody ever found another Oprah. All of the networks and syndicators, all of the thousands of individual stations, all of the talent scouts and agents and agencies never found another Oprah.

Beware of picking the very best, brightest, sweetest cherries when you’re going to cherry pick your argument, because it’s utterly unconvincing.