Random example but I was working with an algae biofuel company during the cleantech boom and we were having analysis problems as the equipment we were using kept fouling due to the harsh desert conditions where our ponds were. I was at a birthday party and obliquely mentioned that issue to a friend who had asked how it was all going and before I knew it, he'd called his former coworker who'd founded a company that successfully launched similar equipment to Mars which was obviously not user-serviceable so was built to be extremely robust. There was no 'ask' from anyone involved and nobody got richer from the exchange, but it was just a random occasion to connect people who might find each other interesting that was completely common in my SV experience.
If you were knowledgeable enough to move to the Valley, if you had the wealth and connections to move to the Valley, then you already passed some of the checks needed to be someone who would be a sufficiently good bet to introduce.
It might already be the case that the Valley has changed to be more similar to the East.
East coast is more of an introduction, with the implied vouch. Setting up a business relationship.