I found 13 tournaments (on ATP tour) for USA. No country has more, actually all other countries have much less:
France:5
Great-Britain: 5
Germany: 5 (I counted World Team Championship but if you don't it's only 4)
Spain: 3
Australia: 3
Croatia: 2
Netherlands: 2
Austria: 2
Sweden: 2
Switzerland: 2
China: 2
Russia: 2
All other countries (that have tennis tournaments) have only 1.
I found 13 tournaments (on ATP tour) for USA. No country has more, actually all other countries have much less:
France:5
Germany: 5 (I counted World Team Championship but if you don't it's only 4)
Great-Britain: 5
Spain: 3
Australia: 3
Croatia: 2
Netherlands: 2
Austria: 2
Sweden: 2
Switzerland: 2
China: 2
Russia: 2
All other countries (that have tennis tournaments) have only 1.
i wonder why they do that... i don't see more reasons to count it twice than for a regular tournament !
in the past, the double masters was held in a different place, maybe it comes from that...