The Asia section (the raft ride and the walkthrough) was supposed to have been an opening day area but was pushed back a year due to budget cuts. The Beastly Kingdom area was also supposed to have been open on Day One, but it was pushed back to Year Three for budget as well (and then killed when the attendance wasnt anywhere near what they had hoped for). Several other large additions, such as large wooden coaster for Dinoland and the completion of the Conversation Station were also cancelled after the park opened. These moves were all down to reduce the capital investment in the park since the original investment was now going to take substantially longer to recoup.
So in place of those major expansions we get very inexpensive stop-gap measures. The Dino-Rama addition was done specifically to counter the complaint that there wasnt enough for children to do (the games financially justified to expansion). The new rollercoaster has been the subject of a bidding war between all four parks for a couple years now. Animal Kingdom gets it because it is the park in most trouble. Magic Kingdom will need to wait for their Villain/Fire Mountain, Epcot will miss its Matterhorn and Disney/MGM wont get their Coney Island Express.
California Adventure followed a similar path but the problems there are more serious. Attendance was down so Armageddon and Rock n Rollercoaster were cancelled to reduce the investment. Then attendance really went south and the kids complaint surfaced again so the cheap Millionaire was put in and some (they really are) shopping mall rides created Bugs Land. But with attendance still plummeting they pulled out Tower of Terror but mostly because its cheaper to build it while they are building the same ride at DisneySea and Disney Studios Paris. Again the pattern is to spend as little as possible to solve complaints about the park.
A park needs expansion when it has too many people for its facilities. Disney/MGM Studios needed expansion because it was so small when it opened (and none of those silly they always build small and fill them out spin lines again that wasnt the case). Obviously neither Animal Kingdom nor California Adventure have problems with crowds. Its impossible to financial justify them based on the current admissions revenue and no one at Disney currently thinks about actually enticing the guests to visit (like a major addition would). They want their money fast and up front.
The last I heard the average guest stay at WDW is just a little over four days. You have to remember that for all you people taking your three week stay at DVC there are a couple of middle class families just trying to squeeze in a long weekend. So the average is just that an average over all of the guests. Your mileage will vary.
It was expected (or the delusion had it) that AK would add a full day on to that stay. A significant number of WDW guests still venture off property for Sea World or Universal or Busch Garden or whatever. Disney somehow convinced themselves that adding another theme park would keep everyone in place along with the water parks, the mini golf, and the bar areas.
Past experience had shown that is what happens when Disney would open up another park. EPCOT Center turned WDW from a day trip into the centerpiece of a trip to Florida, Disney/MGM Studios turned that centerpiece into a destination, the hotels, water parks and Pleasure Island turned the destination into a full-service resort. Animal Kingdom was expected to lock people on Disney property as tightly as if they had been on a cruiseship in the middle of the Caribbean. With four parks demanding four full days and all the other activities demanding at least a full day, Disney was sure it could force a full five day vacation onto its guests.
The problem was people just didnt behave like the PowerPoint presentation said they should. Instead of extending their stays or staying on property, people simply took time away from Disneys other parks and squeezed in Animal Kingdom. Worse, the park itself was not a draw; the public wasnt booking additional trips or visiting more often to see the new place. All of the financial assumption behind Animal Kingdom turned out to wrong and horror of horrors it was sucking the money away from all the existing parks. This was Disneys nightmare and why all talk of a fifth park stopped immediately.
The only thing that went in Disneys favor was that Islands of Adventure stumbled out of the gate as well. Universals park was lost in the overwhelming Disney glow that used to surround Orlando and it took time for it to punch its way through. And Universal quickly learned that simply having two theme parks does not make a resort. You need the hotels and nighttime entertainment and another park to make a resort. It was lesson that Disney ignored as well in Anaheim*.
I assume that use the same first park of the day method that Disney uses (a lot of the management there came from Disney). I have heard that park hopping is very small where at Disney it is a major factor.
* Why the two park worked when EPCOT Center opened is a topic for another thread.
