Yeah, fair point. If by Silicon Valley, you mean the large tech companies (like Google, Apple, etc), you're correct that they won't ask your salary expectations since they have their own internal process for determining compensation for a given candidate. (They also generally think they can outbid anyone else).

I have been working with smaller startups (down here in LA, but I've seen the same behavior up north), who tend to filter candidates based on expected salary due to limited resources and hiring for an exact role. (We tend to mask our cheapness by using phrases like "hungry" or "passionate").