As someone posted above MMO's generally don't have live/random content and even in the case of say WoW prior to Cataclysm everyone was able to do the content if they took the time and effort because the NPC's where always there or walking around town somewhere.
I don't normally like to talk about WoW because I didn't play it but from hearing stories from my friend WoW had many one-time events that you don't get to replay. Here's a link the list is towards the bottom of the page http://www.wowwiki.com/Event. If you look at the list you'll notice that there were many one-time only events that happened long before cataclysm began and some that even lead up to cataclysm itself sort of how we are doing events leading up to 2.0. Also if this is the forums reaction to a tiny event that is barely noticeable if your not looking for it it's probably going to be a sh*tstorm in here when 2.0 rolls around and suddenly everything we are doing right now is going to vanish.