Eventually all communication mediums will be expected to be instantaneous and synchronous. It happened with email, it happened faster with SMS because everyone expects you to have your phone up your ass at all hours of the day.
What really sets it apart is the robustness & cleverness, IMO. While delivery is not guaranteed, it's generally extremely reliable even with awful connections, and from what I remember it piggybacks on an existing communication channel meaning it was a "for free" extension of the original network.