I personally don't get why it is sooooo terrible for people to show up for OOC reasons.
Forgive me for barging in, and correct me if I am wrong... But showing up for ooc reasons punches plot holes in the event. A short example, perhaps:
An event is announced on these message boards that there is going to be a GM event in Ojaveda regarding a rogue uprising. In rp, no one will know of the uprising until it happens, because its secret. Characters who were say, planning on making a trip to the bronze doors, or perhaps needed to pick up a weapon at Hydlaa suddenly have a change of heart saying "Hmm I want to go to oja and hang out for a bit"
For what appears to be no apparent reason, they are motivated by ooc reasons to drop rp in hope they might get some shiny stuff at the event. This means all over yliakum, suddenly people flock to ojaveda, ironically right before the rogues start their revolt. This creates what I like to call "Plot holes" Or anomalies, unexplained events that technically shouldn't happen.
Of course you make a good point, if the game masters could organize events in every major city we wouldn't have this issue would we? Well the problem there is that it takes a battalion of game masters to over-see a single event, to make sure everything runs smoothly, and much of the time a battalion of game masters are not available. This means that the staff would not be able to support such events, well... perhaps once in a blue moon, but not as often as players would like.
Hope this makes some sense.