I did read your full post, and I understand the laws of supply and demand.
If your first idea doesn't work, that would suggest Main/Early is full. How can the $10 surcharge work in that situation? You can't charge a fee for a seating that ihas no space available.
It's not for the "same cruise." It's two alternative plans. In the first plan, you offer a $10 gift card per day per room. If Disney finds that after they have implemented the policy for 1 year, that there is still a shortage of people who voluntarily give up main dining to go to late dining, then they may consider implementing the second plan. Though, as you've sort of proved, people feel much more pain losing $10 than not gaining $10.
As for your iPhone example, it is somewhat flawed. Disney has a limited opportunity to sell a cruise ship. Once it sales, all empty rooms are essentially assets that are forfeited. In addition, the supply of rooms, will never increase from when it goes on sale. Thus, their goal is to maximize the amount of profits for the limited number of rooms.
On the other hand, an iPhone will have limited color quantities, but it will eventually be refreshed. Someone just has to wait. Now they are somewhat time limited in that a newer phone will come out, but all of the excess inventory will not be lost. Instead, they still have robust sales on those (especially for replacements for damaged phones).