I can see microsoft dropping the price of the 360 even if it costs them money for the simple fact that if they drop the premium to say 210 or 220 they could go crazy marketing it around the ps3 launch date as being half the price of the ps3 assuming the premium ps3 retails for around 420.
That big a price difference could make a lot of difference as to which console people buy, particularly parents who likely only buy one console for their kids, in which case a saving of 200 odd pounds is a pretty loud argument for the 360 over the ps3.