What does 这是 ～ 更是 mean?
Why are you digging up such old questions? That was nearly 4 years ago! What a pity my Chinese has not improved in all that time! Pleco is none too good. My advice: first, ask your Chinese friends. Also try Hanping Chinese Dictionary Pro.

这是 ....， 更是 .... this is ..... , but it is also .....

现在，
Nowadays
中国网民总数已经超过美国人口总数，
China's total number of Internet users is more than the population of America,
但美国网购人数占其全部人口的75%，
but America's online shopping users make up 75% of America's population,
中国则只有25%左右，
whereas China's online shopping users only make up about 25% (of China's population)
而且，
moreover,
中国网购消费者年均消费额仅为美国消费者的1/5。
China's online consumers' annual average spending only represents about one fifth of America's online consumer spending.
于刚认为，这是差距， 更是中国电子商务的潜力。
Yu Gang believes, this is a (big) disparity, but it is also China's e-commerce (development) potential.