I agree, it wouldn't be appropriate for them to make assumptions about how the drive will be used. They should report the raw capacity - by which I mean all capacity that's available through the drive controller (but not any internal spare sectors that the outside world can't directly see or use). File system formatting is a higher layer application issue which is outside the scope of what the drive manufacturer can predict or is responsible for.
However, I do object to their misleading definition of a gigabyte. Data has always been properly measured in base-2, unless somebody is selling something. But I understand they have to play this game because if one company does it, the others don't want their drive to look inferior.