If MS thought they could continue selling zunes at $249, they would have.
I think you are spot on cellocello. Not only does heavy discounting mean no profit for Microsoft, it hurts the perception of the product with retailers (and customers). Heavy discounting results in a race to the bottom, with the chance that no one makes any money. This is likely the reason that Costco dropped the Zune - they could no longer guarantee to their members that they offered a "good" price. Consumers begin to wonder if they were ripped off by buying at a higher price following heavy discounts (look at the uproar over the iPhone price cut).