Emily has the answer - I read recently that Disney is concerned that the passes are too cheap. This encourages lots of locals to buy them, which also mean they go more often.
A few years back when Disney was struggling this sounded like a good idea. Now the parks are doing well and crowds quite high, they would rather have more overseas and interstate holiday makers paying for 3 and 5 day passes, than locals adding to the crowds effectively for free most days.
Also, as the interstate and overseas tourists are often doing this as the one trip of a lifetime, they are more likely to spend a lote more money in the park on souvenirs etc. So, financially it makes more sense to make it more attractive for them, and more expensive for the APs.