I don't think that's it. That's what the UI on Windows Phone and Surface looks like, so I'm guessing it's intentional.
Personally, I am fucking sick of rounded corners, so seeing the right angles here really made me happy. I'm guessing their designers felt the same way.
Rounded corners are known to draw attention inward while angular edges "point" outward, which could make rounded corners a better choice for content containers from the usability perspective. An interesting discussion on the topic here: http://ux.stackexchange.com/questions/11150/how-do-rounded-c...
OTOH, I love the feel of Metro and wouldn't change to rounded corners for the world.