You're fairly limited in terms of antenna size/placement when you use a tiny dongle. If it's built into the Pi, they could have the antennae wrap around the edg

You're fairly limited in terms of antenna size/placement when you use a tiny dongle. If it's built into the Pi, they could have the antennae wrap around the edge (similar to how the iPhone does it) to allow for a much higher quality connection. At least, that's what I hope they're doing with it.