Similarities with event-driven programming

Wikipedia defines reactive programming as follows:

"A programming paradigm oriented around data flows and the propagation of change."

The very first thought of this may imply some similarities to a well-known event-driven programming. The data flows and the propagation of change sound a bit like something we may implement via the \SplSubject, \SplObjectStorage, and \SplObserver interfaces in PHP, as per the following trivial example. The \SplObjectStorage interface further encapsulates the \Countable, \Iterator, \Traversable, \Serializable, and \ArrayAccess interfaces:

<?php

class UserRegister implements \SplSubject
{
    protected $user;
    protected $observers;

    public function __construct($user)
    {
        $this->user = $user;
        $this->observers = new \SplObjectStorage();
    }

    public function attach(\SplObserver $observer)
    {
        $this->observers->attach($observer);
    }

    public function detach(\SplObserver...