PS3 has played all their trump cards almost (slim, price reduction) and only have one left - GT5. GOW3 etc will sell 4 million but they will not be system sellers as people who want these generic games already have a PS3, same goes for Halo Reach on the 360....it will selll 10 milllion but won't push systems for more than a week or 2. So basically the gap will not really change and we can see that as it is basically still about 6 million. 360 if they bring out a slim will help sales but the gap will still hover around 5-7 million until both consoles are replaced. The motion devices for both consoles will do little as they were not included from the start and so will have limited support...a few games but most won't buy into it as the hardware did not come originally with the console so developers games will still be aimed at the 30 million+ consoles that don't have motion support.
As for Wii....well we all know it won the generation, well done Nintendo.