I think this is a good point. Both are about equally true. Around half of Russian economy lives in Moscow region, formally or informally. About half of the world's startup ecosystem is in North California. Everyone else just makes do with what remains, or moves.
I remember from "Founders at work" something like: "West Coast is the land of dreamers" and something about how it totally opposite with Boston and NYC (I don't remember who said this)
And I suppose that this is possible.
But:
There is "life outside MKAD"
Even with:
"Around half of Russian economy lives in Moscow region, formally or informally" - I remember that 75% of all money in Moscow
In Moscow a humorous proverb exists: "There is no life outside MKAD(http://en.wikipedia.org/wiki/Moscow_Ring_Road)
When I read PG (and others) about "there is no opportunity for [startups ... interesting productive life] except SF" - I think it's the same. Not true