Worked for me. It's not for all items. Adding something to your dreambox doesn't necessarily mean you're going to get the discount.
I think it only works for U.S customers.
Can you tell me how to buy from the U.S store if you live in the EU?
Was it in 2 weeks time last year that the winter/holiday sales occur? I do recall 40-70%ers but I've forgotten in the past year.