Americans help me out with Mustang engines

Now I live in Australia and car manufacturing is dead here, it killed itself (ducks for cover). On the plus side it means we are getting the 2015 mustang. I'm actually genuinely interested in this as a car.

Specifically i'm interested in the ecoboost. Now I know its semi-sacrilegious not to get the v8 but I like the new tech and the improved fuel efficiency etc.

But here is my question...why a 2.3l 4 banger? It doesn't make sense to me. I just read the article on Jalopnik about the new truck (F-150?) and that comes with a 2.7 v6 and a 3.5 v6 ecoboost. For me both of these engines seem far more sensible for the mustang.

Can anyone help me out with why they weren't used? Or does anyone know about interchangeability?

Cheers.