Not that I put much weight on those numbers, but since they've been posted and used as a basis for comments here, I'll use them too.
Civic and Corolla have been the benchmark for fuel economy in this class for a long time and if GM used any competitors as benchmarks in their product development process, I bet those two have been included. So let's see how they compare (use the Cruze model believed to be the volume seller):
Civic 1.8L: 8.2 5.7
Cruze 1.4L: 8.5 5.5
Corolla 1.8L: 9.4 6.5
By the numbers, it looks like GM had surprisingly succeeded, despite Cruze being a much heavier car (quieter, better ride and more solid feel too).
Sure, the new Elantra is raising the bar and I would give Hyundai full credit for doing that, but this is normal. I'm sure Toyota, Honda and others will not stand still and the cycle will continue.