That did seem like a strange omission, agreed. Neither is quite what we would traditionally have called a 'city', though - Tokyo is an entire prefecture (aka state, or province, depending on how your country divides its regions), the PRD is a Gibsonesque Sprawl of huge cities and smaller ones. So while I agree with the general premise that these are the largest urbanized areas in human history, we will need to revise our terminology to call them cities (or they'll need to implement a single local government, tax structure, address and street naming, etc. to fit the exiting definition).