does every airport has its one liverys for the trucks etc?
Well, not *every* airport, because there's no such thing in real life too, but we have many liveries, both for service and catering operators, and they are varied around the world according to a reasonable distribution.
Of course, there's nothing inside GSX that prevents to have each single airport with its own vehicles, both in modeling and liveries, so we can easily add new models/liveries or change specs regarding what appears and were.