I disagree with the statement about people just going from where it is cheapest. There are of course some who do but also many who would happily pay extra to fly from their local airport. This cost is usually made up for as fuel and parking prices are far less, as Taxis and Public transport are normally quite cheap over short distances and many people get lifts from friends and relatives, which usually costs them nothing!! Plus the actual transition through the airport is far quicker and easier at a local airport like SOU or BOH than congested hubs like LHR and LGW.