jpthomas72 / AndyH52,
I am not in disagreement with you. Many airports serve cities which have substantial populations, administer a region, or have historical claims to capital city status. As do the German examples listed by jpthomas. But still, they are not capital cities today. That is the point. Whether or not they are the seat of government today is incidental for the purpose of exploring their potential for profitable air services. "Capital City" is a concept best left to politicians and their cronies. "Prosperous Conurbation" is of far more interest to the economics of the airline industry. And Greater Manchester is a prosperous conurbation supported by other similar population centres nearby. So lets not get distracted by the capital / regional labels. Successful airports can be located in both capital and provincial locations.
By the way, the New York x3 was not a reference to population size; I was alluding to its support of three major airports in JFK, LGA and EWR. I should have expressed that point more clearly.
Ian Brooks, you are right to acknowledge LH's support for MAN. Unfortunately, they do not currently offer a hub-and-spoke operation at MAN in the way they are able to do at MUC. That is not a criticism of them; it is simply the reality of the marketplace at the present time.
SHED.