That is true. I wasn't aware of this. I redeemed TY points for an international flight on Korean airline thinking that I could transfer those miles to delta. However, the inventory that expedia had at that time for my flight was in class Q. With this class, I can only earn 70% of miles on Korean but I cannot transfer them to delta at all. So be careful.. just check your booking class before making a reservation. It should be okay if your flight is with US-based airlines...