Google left, Facebook is blocked, Amazon is struggling to make headway. And if further proof were needed that China’s tech market is a world apart, this week seemed to provide conclusive evidence. Uber, a ride-hailing service that is the world’s most valuable startup, decided to sell its local unit to Didi Chuxing, a Chinese rival. Chinese firms are protected from external competition by government regulation and the Great Firewall. And that protection means that they need not innovate but can thrive by copying business models developed in the West. In short, China is closed, its firms are cosseted and their talent is for mimicry.