This table here shows how price cut and new devices release affected the sales and Gap of HD consoles. I didn't take the release date of 360 Slim and Kinect and Move into account since the 360 Slim was still selling at $300, no price cut there.
The Event | Event Date | 360 Total | PS3 Totals | Gap at Time |
Before PS3 release | November 2006 | 5.16 Millions |
0 | 5.16Millions |
Before 1st PS3 price cut | November 2007 | 12.74 Millions | 5.68 Millions | 7.06 Millions |
After PS3 price cut and before $200 360Xbox |
September 2008 | 20.00 Millions | 14.32 Millions | 5.68 Millions |
After $200 360 release and before PS3 Slim |
End of August 2009 | 31 Millions | 23.07 Millions | 7.93 Millions |
After PS3 360 Slim, Move and Kinect till today |
16th April 2011 | 53.11 Millions | 49.51 Millions | 3.6 Millions |
It should be interested to see what will happen after a new price cut from those consoles.
Edit:(corrected PS3 sales in last lines thanks Zgamer)