Mathematically, it is the same as going from 20% to 14%, which is pretty much what they did to indies on iS. If you take account of the fact that some sales were already at that level, it might be more like going from 20% to 16% or 17% which, I suppose, is the sort of loss that they have determined most photographers will swallow.
I suppose our basic problem is that since we have already done the work against the hope of future payment, it becomes difficult to say we would rather take nothing at all than accept a less than we expected. Psychology is always on Getty's side.