Microsoft has been in a better position to drop the prices of their SKU's for some time, they haven't because there was no concern Sony were going to lower their prices.
I wouldn't make the mistake of assuming Microsoft could not, would not lower their prices as well to retaliate.
i am not so sure that MS wont lower their prices too with some new model.... i doubt they are doing nothing.
We know they are planning a $400 Halo 4 unit for November and it was not a new model. They could change their minds on price but no new model this year.