Earlier quoted context omitted.
The multitude of world changing organizations, especially by market cap, that have come out of SV is some evidence. Not that that means “best of the best”, but if I were to bet on where something transformative will come from, SV would still be on my short list. It’s all about playing the odds, not necessarily being absolute about statements like best of the best.
There aren't many "world changing" organizations coming out of SV lately, and I'm not sure that claim holds in any case: http://fortune.com/fortune500/visualizations/ Even narrowing down to "tech" companies, there are enough outliers that I don't buy it. Change it to "SV has the best developers searching for VC funding," and I believe it, but I'd still question the cause and effect of the situation...
Older companies like Google, Oracle and so on still contain pockets of tech excellence, but you can't buy those guys with your startup idea.