This is what Felix told me by email. This is actually what I thought - these are price reductions before final payment.
As long as it is before final payment and you qualify for the reduction (ei not a Tuesday special) they will give you the reduction. I believe when they first made this announcement they didn't intend to give any reductions but quickly discovered that wasn't going to work.
That would only have created masses of paperwork with cancellations and rebookings. That would have killed them and murdered us as Travel Agents.
Once final payment has passed thats when the no price reductions kicks in. That is primarily because that is when the biggest reductions are usually posted. At final payment its not unusal to get a lot of cancellations as people discover they can't afford to sail, don't want to sail, have been holding other cruises while they decide what they truly want. With that in mind, they have sales after the final payment when they know how much stock they really have.
If you book after final payment that is when you have 48 hours for a reduction. There is only a slim chance of that happening so they're willing to take their chances.