I know Atkins recomends measuring things like spinach raw. It just seems odd that frozen spinach would have that much of a descrepancy, unless they measured frozen. Typically I can measure out 2 cups frozen, cook it and get 1 cup, then press all the moisture out and end up with 1/2 cup.

freckles if they're doing it by volume (yuck! at least everything in the UK is done by weight in g, not cups, or oz!) they can know that when you get it out of the packet it has a certain volume. If you microwave it, or boil it, or fry it or whatever, it's likely to reduce in volume by a different amount for each cooking method, and potentially the amount of time used to cook it, therefore they're giving you the measurement in the known state before you've cooked it.

Makes sense if you think about it!