If Microsoft cut the price in the US, Sony would follow and do the same; thus having no net effect. I might actually help Sony more, as the PS3 is the new standard for Blu-Ray players. Microsoft knows this. Sony would not let their current US momentum slip away. This is not "conceding defeat", this is just the reality of the market. MS already has a huge lead in the US that Sony may never be able to overcome. MS is hoping GTA4 gives them the sales bump that they want.
MS/Sony will not drop the price in the US until after E3.