Bear in mind the 360 and PS3 are both selling well but the 360 is not selling as well as the PS3. Dropping the price of the 360 in USA around the launch of GTA 4 is a foolish move, people will get 360's and PS3's regardless if there is a price drop. To pick up an extra half million console sales for the sake of a price drop is a wrong move.
360 price drop may come before the launch of MGS 4, probably when Ninja Gaiden 2 arrives on the 360.