According to their 2012 infographic, the single journey that is most undertaken by airborne humans is the 290-mile jaunt from Seoul to Jeju Island in South Korea. According to the FareCompare website, there are 153 flights per week on this route, and well over 40,000 seats available (about 250 people per flight - do those maths add up?). Anyway, ten million people a year want either to get on or off an island in Korea with no small amount of enthusiasm.
As you can see, New York-London doesn't even trouble the top ten. The busiest air routes in the world are all relatively short haul, nipping between destinations that probably have inconveniently-placed natural phenomena between them such as ocean or marauding volcano monsters (they're a thing, right?). And as even the unobservant layman can see, the only international flight on this list is Hong Kong - Taiwan, though some delegates of the Chinese commission may naturally question the logic of that statement.