I think that MS temporary pricecut+ deals was a double edged sword if you know what i mean.
Yes it helped Xone in USA for two inportant months ,but at the same time,it changed the consumer's perception about Xone's "value"(i don't know if that is the right word sorry :P).
In other words,Consumers don't think 399 is a fair price to pay for Xone anymore.