[icebraining]

All of those offered, at the time they appeared, a completely new service that had essentially zero competition, and have become entrenched since then (can you even e.g. get a job without a phone number?). Not to mention that the USPS is mandated by law to exist, so it can hardly be compared with Facebook.

Facebook never offered anything so revolutionary. It's just a well put together implementation of something that was already possible.