Honestly I haven't done any analysis of this, just going off a gut feel. When I look at this data my claim seems to not be true:

http://ssti.org/blog/useful-stats-share-us-venture-capital-a...

But there are programs like Google Demo Day and Rise of the Rest that are reaching beyond SV for value. Several accelerators trying to copy the YC model have emerged across the US - in Atlanta, Chicago, Austin, Detroit, Raleigh-Durham, Boulder, etc.

https://events.withgoogle.com/demoday/siliconvalley/

https://www.riseofrest.com/

The other day Capital Factory in Austin announced they are kicking off a program pulling Austin, Dallas, Houston, and San Antonio under one big startup umbrella:

https://austinstartups.com/the-texas-startup-manifesto-42f06...

Without digging more I don't have much else to say on this :)