It's the "largest game in the series" and time for extra polish couldn't be passed up. Some gameplay for Age of Wonders 3 was at GDC 2013. Minecraft's Notch is funding the game.
It's been a "dream come true" for the Dutch studio to have the creator of Minecraft pump his own money into the project, and "didn't insist on owning it" like publishers do.
"When announcing the game earlier in the year we listed a projected release date of fall 2013,” community manager Jimmy van der Have on the Age of Wonders 3 website. "We immediately got questions on this, whether this would be fall in the southern or northern hemisphere, and when pre-orders would start."
"We’ve made great progress developing the game and feel now is the time to give you heads up that we will take a bit more time creating all the features and content. Age of Wonders III is the largest game in the series and with the additional polish we hope we can give you an even better experience!"
Triumph is now aiming for Q1 2014, but they'll be "organizing several events and are currently planning a great pre-order promotion", and a press-only showing at Gamescom in Germany this August.