I seem to recall reading that it is, but I'm not sure.
To clarify, when you're in a zone can you only see what the other people in your instance are saying, or can you see what everyone in your zone is saying regardless of instance?
It's instanced. Sometimes my partner and I will log in and find ourselves in two different instances of the same zone, and the chat is always different.
If you're trying to trade through zone chat, the usual method seems to be to post a short ad for it, such as "WTT [whatever] for [whatever], PST," then jump to another zone and repost the ad, then jump to another zone, etc.
During an event, focus on the zones that have the Impresario, since those are the ones players go to for spending their event tickets, as well as any zones with event-related destinations-- in this case, Undaunted enclaves and whichever zones the daily pledge dungeons are in.
They should really combine zone chats, or at least let you know what partition you are in.
Even EQ was able to do this and more (like creating your own CHANNELS and having cross-server channels for class/dps discussion, or same server for trading) and that game came out in 1999.
Thanks, @SeaGtGruff - that sounds awful! I was mainly asking because I see lots of people talking about the downsides to pugging and it made me wonder why people don't request specific groups in chat more.