This past week and next week will most likely be the maximum (I believe) sales difference between the xbox360 and the PS3 (and Wii for that matter). Most of the smarter buyers are postponing their console purchases until black Friday and beyond. There you will have a ps3 with an average selling price of $199 and a Wii with an average selling price of $99. And with major retailers not matching black Friday ads (Walmart), it'll be kinda stupid to buy now and try to return later for a bf price. The 360 will have numerous deals but the two consoles will siphon away sales.
I still tend to believe that a good chunk of x360 sales are coming via promotional sales. Many radio stations in my market (DC metro) are giving the x360 kinect bundles are call in prizes, wouldn't surprise me if its a nation wide trend since most radio stations are owned by a total of 5 companies.