I made some changes because the old statistics here raised some questions. Instead of the original 14 cities, there are now 18. The methodology for the Jetpunk statistics is not uniform, so I now use the source citypopulation.de
Buenos Aires is incorrect, population within city limits is 3.1 million, urban area is 13 million, yet it's counted as a 10+million capital city. Seoul is 9 million within city limits, correctly counted as a capital city with a population below 10 million, but the urban area is 22 million. What's the criteria?