请教一个问题

As the etched lines on computer memory chips have become thinner and the chips’circuits more complex, the power of both the chips and the electronic devices they drive has vastly increased

Antarctica receives more solar radiation than does any other place on Earth, yet the temperatures are so cold and the ice cap is so reflective that little of the polar ice melts during the summer; were it to do so, the water levels of the oceans would rise 250 feet and engulf most of the world’s great cities.

为什么第一个可以省略了动词 第二个不能省略动词??????????