Surely the fact that a huge portion of startups start in SF could account for the fact that a huge portion of winners came from SF? You're also biased because you're paying more attention to startups in SF - the Bay area doesn't even come up with half of the big startups, and yet you failed to name a single one from anywhere else.
A quick scan of Fortune's unicorn list* shows 12 out of the top 25 are from outside of California, and two of the Cali ones are LA, bringing SF down to 11 (after generously counting Palo Alto in SF, because I assume you meant the Bay Area). Without numbers on how many startups are started in various places, I'm not sure what these numbers mean, but it doesn't obviously favor your winner-takes-all argument.
Of the top 25, only two American companies are not in the Bay Area, and one of those is still in California.
For an area with less than 2% of the country's population, that is overwhelmingly dominant. I'm not sure if you could have underscored my point any more succinctly.
Somehow you've managed to miscount the numbers, misrepresent your wrong numbers, and miss the point all at once.
The point is that you still have contributed no idea of what portion of startups are starting in SF. If 95% of startups come out of SF but only 80% of winners do, it still has an overwhelming majority but is by the numbers a terrible place to start a startup.
Of the top 25 international, only about half are American, so stop pretending the denominator is 25 if you've decided that international companies for some reason don't count. There are 2 in LA, one in Boston, and 1 in NYC (what list are you looking at?), giving the Bay Area something like 2/3 of American companies, and about 1/3 of all.
A quick scan of Fortune's unicorn list* shows 12 out of the top 25 are from outside of California, and two of the Cali ones are LA, bringing SF down to 11 (after generously counting Palo Alto in SF, because I assume you meant the Bay Area). Without numbers on how many startups are started in various places, I'm not sure what these numbers mean, but it doesn't obviously favor your winner-takes-all argument.
* http://fortune.com/unicorns/