Great marketing idea, doubtful value in practice.
When down is being prepared for sale it is washed to make sure it is 'clean' - no lice or insects or whatever. But a good down supplier will not strip all the natural body oils out of the down: they will leave a fair bit of it in. This body oil is a natural DWR used by the ducks to keep their feathers and down dry. In fact, when ducks are 'preening' they are actually spreading that body oil through their feathers.
Somehow I doubt that what they are adding will match what a million years of evolution has developed.
I also question the ethics of the advertising. Good down does float on water, and does not immediately turn into a wet soggy lump. When properly dried out a washed sleeping bag usually has a lot more loft than before the washing, not some small percentage. To suggest otherwise, per the advertising, verges on being deceptive.
Mind you, if you scour ALL the natural oils out of the down, then you have a problem. The best solution is to not do that.
PS: strong and accurate analogy with partially scoured wool: it too is 'waterproof'.