I work at a youth centre. The teens I know really have the widest range of options of contacting each other. They use FB mostly for school and family. Email is used mainly for sending documents or attachments.

If they're hard to reach it's because they chose to, not because you're using the wrong comm channel :)

How is your guess about other people useful info?

How is the parent comment's guess about 100% of people having email useful?

That it is true, and a communication system?

But if many don't use email much, how does it help? I barely check my personal email. And no one in my normal life knows my business email. Once in while a family member or friend will send something unimportant via email. Either I never see it. Or I see it a week or month afterward. My career relates strongly to the internet too.

If you don't respond to email and I don't communicate with you in person or on the phone I assume you are uninterested personally or professionally and take my friendship or business elsewhere.

Answering email is really a pretty normal expectation.

So is facebook for friendship lol

If you ask for their email and they offer to friend you, and you decline, should they assume you don't want to be in the loop for things?

Your arguments for email as a platform equally apply to facebook. Yeah email is decentralized and oldsr, but that stuff doesn't matter to regular people who want the easiest tool for the job.