This is the only quote I can find regarding Garrisons and gold: "Garrisons have their own resource, more on this soon!"
https://twitter.com/Muffinus/status/446808409736634368
But if you check the screenshots from PAX East, you can see that upgrading costs gold. Like this: http://media.mmo-champion.com/images...nWoWRAD013.jpg
Very confusing.