March 2009 (UTC)
An event horizon is any surface from beyond which no information can ever reach the observer.  Of course, that includes objects of all kinds - in fact, anything moving at or below the speed of light - so in a sense you're right.  An important thing to note though is that the event horizon - in the strictest sense - belongs to the observer, rather than the thing (not) being observed.  In the case of a black hole, the event horizon is the same for all outside observers, which I guess is what you mean by a 'physical boundary'.  The Event horizon article is biased towards this, the most commonly encountered form of event horizon.  The cosmological event horizon is different: since every point in the Universe is receding from every other point with a speed proportional to distance, the event horizon is always a sphere centred on a particular observer, so there is no single 'event horizon of the Universe' (although of course we tend to give a special place to our own event horizon).

So neither article is wrong, although the introduction to Event horizon gives a misleadingly narrow interpretation of the term, which I'll try to fix.  The cosmological use is however mentioned in Event horizon#Event horizon of the observable universe.  There are more details in Cosmological horizon and Particle horizon.

  13:10, 6