I suspect its the 45nm RSX + either lighter PSU or lighter fan+heatsink or both. That'd probably explain the differences, I suspect perhaps they had a little trouble taping out the RSX GPU and they ran out of supply of the 65nm version.

Maybe we just have a different definition of the word gimmick cuz I'm still not seeing how it's a gimmick... The console was redesigned to be cheaper to produce(thus the price drop) and smaller in size as well as weight which are both very desirable attributes for an electronic device. It also uses less power and is quieter than the phats which are again desirable attributes. If some people have the money and can purchase another PS3 for those desirable attributes then that is not just a gimmick. If they were buying a second PS3 just to store in their closet then I may agree with you that it is some sort of gimmick but that is not the case. And even then the rebuyers are probably only 1% of the total market so they wouldn't be the group of people to brand something a gimmick or not. 

More parts made up of aluminium?
That's a good way to make the PS3 costs cheaper and profits a little better.

PS3go?

200g lighter? Maybe they're giving out a dvd instead of a manual? Or no controller :P j/k

the official PS3 Slim will launch 2011 with $199 or $249 price tag.

notice how sony doesn't call this slim??

Smart move and just another of many more to come. SONY is a HW comany after all, no?

Don't get me wrong, the console is better, there's no argument about that.

The word Slim though is just a marketing word now.  As I said earlier it falls right in line with RPG Elements or any of those other back of the box words and people eat that up.

It's not just a marketing gimmick it's a distinct name to distinguish the slim models from the phat models. You keep distinguishing them yourself by saying the slim models are better, yet you expect Sony not to distinguish the two types of models by the name?? It's not a gimmick just because it helps sales. That's like saying diet coke is a marketing gimmick. They should just call it all coke and people could just guess whether it's diet or regular when they buy it. 

Diet Coke isn't just the next evolution of Coke though, you can still buy Coke.

You can't buy the old PS3 because the Slim is the PS3 now.  There's no point in saying PS3 Slim unless you're just talking about the differences between the two because the PS3 Slim is just the evolution of the PS3.  The PS3 is the PS3 Slim.  I don't expect them to distinguish because there's no point.

Do you see Microsoft call their 360's Xbox 360 Falcon and Xbox 360 Jasper?  No, there's no point because as soon as they made one, they stopped making the other. 

It really is just a marketing gimmick.  Sony knows that when they introduced the PS2 Slim and branded it thus, it was a good deal because it fixed many problems and came with a price drop.  People liked that.

They did the same thing with the PS3 and branded it PS3 Slim because that meant people would expect the same.  They knew that if they just called it PS3 2.0 or even just the PS3 it wouldn't be nearly as big of a deal.  Calling it Slim though, fanboys everywhere immediately started drooling.