I'm pretty sure it's just really well recorded. The voice changes in tone to emphasize different words, which isn't a feature in any text-to-speech program I know of.

All that said, every time I read a comment in this thread, I hear it in that voice now.

Video was by the good folk at http://www.wyzowl.com/ I am pretty sure it was a genuine voiceover but might be wrong!

I'm pretty sure it's not. I'm interested in TTS and have never heard anything that good yet.