Which phone do you have? I suspect this could be disabled on older iPhones. I have a 4 and I don't get any voice feedback.

I tried it on iPhone 4 as well and it does speak some answers. Touch the "i" button on the left of the red microphone button and make sure "Speak answers back" at the bottom is turned on.

Interesting.

I can the "i" button in that video, but my app does not have it, and I don't get voice answers.

Edit: Switching to English (US) does give vocal answers, but then it doesn't seem to understand my South African accent anymore.

I am on the iPhone 5

For some reason I had English (Australian) active in the Google language settings even though I don't live there. It started reading the answers when I switched that to English (US).

Yes, that did the trick! English (US).