GW2 is all about being dynamic. Dynamic events, vendors, etc., however I feel that the wiki is much less so and we (the community) probably have mostly ourselves to blame. The wiki and community are still young and I believe that both will be more well-rounded in the coming months. Currently, however, the amount of relevant content is lacking.
For example, my most recent encounter was with the vendor of Bauble Bubbles. The wiki still indicates that they can be turned into the merchant from the event in Rata Sum for various items, and although the vendor is still there, he no longer offers items in exchange for the Baubles. His own page on the wiki also makes no mention of the fact that his services are no longer available.
I'm just as guilty as anybody for not rectifying these things (such as the above), but if we want the wiki to be a good source of truth for the game, they need to move in sync. I think community awareness posts such as this one are a great start....