The data in this chart doesn't say anything about the size of the hub, the total passenger boardings, or the size of the local market.
This link contains some of that data.
http://en.wikipedia.org/wiki/List_of_the_busiest_airports_in_the_United_States
All the chart 700 cited shows is that the cost to board a passenger at CLT is the lowest of any large airport. The cost per passenger boarding is a cost to the airlines which just means that US pays very little to board passengers at CLT. Part of the low cost is because the physical structure of the CLT airport is a lot smaller than comparable airports but a lot of it is related to the fact that US has pushed a lot of traffic thru an airport that wasn't necessarily designed to carry that much traffic and therefore the costs are low; CLT is also very efficiently run. Cost per passenger is also low because connecting passengers count in passenger boardings but they use very few services from the airport. All a connecting passenger needs is a bathroom, perhaps a restaurant, and seats at his departure gate - plus the infrastructure that US needs to operationally handle that passenger (bag sort/tug areas, ramp control, employee offices/breakrooms etc.)
ATL as a local market is almost 3X larger than CLT and the DL hub at ATL is about 40% larger than AA's hub at DFW, the second largest hub in the US - but that information isn't in any of the two articles above but it does provide perspective on how CLT ranks relative to other large hubs - which many people here continue to bring up.
All that really matters for this conversation is that CLT's high percentage of connecting traffic COULD be a liability to the combined AA/US network because connecting traffic is not as profitable as local traffic since the passenger has to be handled more than once.
OTOH, US has the advantage and AA/US should retain it that CLT is a much lower cost hub than MIA for connections but MIA is not a terribly large domestic connecting airport now - driven by geography; CLT predominantly handles connecting traffic which is why DL's hub at ATL is CLT's largest competitor. AA carries a lot of Latin America connections thru MIA and the higher costs are not as big of an issue because the ticket price is higher. Still, CLT should be an attractive airport that AA/US could use to grow Latin America traffic because of the low costs of the airport, even if the local market is relatively small. AA's presence in Latin America will help CLT be able to develop new traffic to Latin America.
In the NE, PHL is a lower cost airport than JFK per passenger but PHL also does not have a local market the size of NYC. US pushes more connecting traffic onto its international flights than AA does in comparable markets from JFK. Obviously, PHL and JFK compete with EWR and IAD in the NE and PHL compares fairly well to those hubs in terms of costs and local market. Remember than EWR has a much higher percentage of connecting traffic than LGA and JFK do.
The challenge for the new AA is that if you start pulling the connecting traffic off of AA's flights at JFK or MIA and rerouting it thru lower cost hubs, you have to replace that connecting traffic w/ local traffic or you run the risk of the hub size shrinking, allowing competitors to take a larger share of the local market.
Pulling off connecting traffic also pushes up the cost per passenger for the passengers who remain. Most of the costs for operating the terminal will remain but if there are fewer passengers going thru the facility, costs per passenger will go up. AA's facility at JFK already has very high costs per passenger in part because they are not pushing near as many passengers thru it as they thought they would pre 9/11 when it was planned. In contrast, B6's costs per passenger are probably the lowest at JFK in part because they don't use widebodies.
Esp in NYC where AA is the 3rd largest network carrier and #3 at JFK, pulling connecting traffic off of AA's flights to route it thru PHL is a potentially risky venture.
There is a greater chance you will see new Latin America flights added to CLT to overfly MIA than you will see AA by choice rerouting connecting passengers from JFK to PHL unless competitive changes dictate otherwise.
