Well, I havenít noticed this problem.
I have a 1977 550proof down sleeping bag (0F rated) that still lofts very well. It has been washed once.

None of my WM 850proof bags have lost loft and they have seen a few hundred nights in them with my family since 2003.

In 2004 I bought a WM Flight Jacket (850proof). I wear that jacket about every single day for 6 months of the year because of global cooling frown. So that jacket has seen 900+ days and it still looks new and fluffed. It has been washed once. I dry it out by riding my little Honda scooter at 70mph. Talk about fluffing it up! It handles 20-50F weather very nice.

I have a JRB Stealth 800proof quilt. Iíve been only using that for the last 8 months. It still looks good but the jury is still out on that.

And this place http://www.idfl.com/articles/Fill%20Power/IDFL%20Fill%20Power%20Questions%20and%20Answers.pdf can return a 5 year old bag in cold compressed storage to its original loft!

Iím just wondering if the down you have somehow lost its natural oilsÖ

-Barry