The Slim release was because people holding out were given a new model a 100$ price drop to send them flocking to buy this. What reason would the 360 have? The 360 selling as much as it has - is impressive. Microsoft cannot be stopped, no matter how many people proclaiming thier business and console doomed or in trouble. Fact of the matter is - even if they ended up third sometime this century, they're making Sony break thier back - with Sony throwing every pitch they have in their arsenal.
Face it - Microsoft has made Sony - former #1 in the business - writhe and squirm in the pain of competing in the HD console war. Deny it all you'd like - they did it.