A lot of big projects have been happening at the World and a lot more still to come. Looks like those costs are being passed down to the guests, as with most things in life.
Base one day tickets have increased by $4. Bringing a one day pass to the Magic Kingdom up to $99. I don't think anyone could say that the cost unjustified. In comparison Universal Studios os charging $92 a day for either of their parks. Perhaps after Diagon Alley that could go up as well.
Touring Plans has a great break down on how the increase affects multi day tickets in every combination.