Already the growth has been explosive since the Slim version was released and some of the system's most important titles were released and many users that previously didn't think of the PS3 are now considering it. This would be boosted by dropping the price further.
Microsoft's answer is supposedly all on Natal and it is still to be seen how the new control scheme breaks in the market since we can know what to expect of Sony's Move. We can believe that Microsoft will probably have a thing kept from us or two... maybe the rumoured Xbox 360 Slim? Believe me Bill, that would be a smart move.