Probably because the way things are now, very few people actually buy a regular one-day ticket. A lot of people have multi-day tickets or vacation packages, which are cheaper. Then there has been the Summer Fun pass this year for $99, which breaks down to $33 a day for each park. Disney will still have deals like that going on because of the economy and to make sure attendance does not take a dive. But they will still bring in more money with the higher AP prices and those who do buy just one day regular tickets. I would think as long as their attendance figures do not take a huge drop, they will continue the annual raising of prices. Even so, I remember when they only raised them $1 a time. How many more years until it is $100 for a one-day, one-park ticket?
The $20 renewal discount probably will not change. I would bet they factored that into the $40 increase for Premium passes.