I agree with you that PMs have to use charisma and influence to get things done, but I completely and utterly disagree that they are more "expendable." A good, certified, educated and experienced PM is worth a dozen engineers. You can find engineering talent almost anywhere - but good managers are a diamond in the rough.
I've been a PM for about a half decade now, and was previously a software engineer for some big name companies. I'm telling you, PMs, if they know what they are doing and are educated properly, are worth their weight in gold - because writing code can be outsourced, management can't.
Maybe it's different in Silicon Valley (which would explain a lot of the risk-taking, lax attitudes and failure rates of startups), but the rest of the country is the opposite of what you describe as the "expendable" PM.
I've been a PM for about a half decade now, and was previously a software engineer for some big name companies. I'm telling you, PMs, if they know what they are doing and are educated properly, are worth their weight in gold - because writing code can be outsourced, management can't.
Maybe it's different in Silicon Valley (which would explain a lot of the risk-taking, lax attitudes and failure rates of startups), but the rest of the country is the opposite of what you describe as the "expendable" PM.