The main reason IMO is that all the advantages the CELL has over a traditional CPU (highly parallel, great floating point performance etc) a modern GPU does 10x better. The GPGPU revolution of recent years has meant that modern GPUs have gained general purpose computing capabilities, which allows developers to utalise hundreds of shader cores in parallel which is great for things that require lots of simple repetitive calculations, things like rendering, decompressing video, and even physics simulations.

And those are all the things that the CELL was designed to do by using several SPEs in a time where CPUs had at most 2 cores this meant that in those areas the CELL beat out any other CPU at the time (and still outperforms the latest CPUs in some areas), which meant that developers could use it to do graphics work etc in conjunction with the GPU in the PS3. But the CELL was also weaker in many areas compaired to a traditional CPU, and with the huge advances in GPU computing the CELL is basically obsolete which is why IBM abandoned it. 

Also upgrading a CPU architecture is not an easy task, compainies like IBM and Intel spend hundreds of millions of $ every year upgrading their CPU architectres, while they also spend tens of billions over several years making new ones. And as IBM rolled the CELL team onto other projects the CELL line has been left alone. Sony doesn't have a full CPU design team in house so they would need to pay IBM to upgrade the CELL to meet modern standards which would likely cost millions. Licensing a modern CPU and a modern GPU would likely not be much more expensive as they would require less modification and would likely end up being much more developer freindly (the CELL is notoriously hard to work with which meant only 1st party studios that could devote years to mastering it could actually get good resaults from it). 

The only reason to go for the CELL again would be for backwards compatability.

At $499 I dunno if itll be a success in America but €499 was also the launch price for PS2 in Europe.

I hope thisll be the launch price, I dont want Sony to compromise on hardware. I really want 1080p@60fps with atleast 4xAA next gen.

To be honest this gen is getting boring pretty quick. Thank god there is still some fresh games like Beyond, NiNoKuni and The Last of Us coming out becoz I cant stand all these sequels with the same mechanics and graphics. -_-

Neither can I! That's why I'm happy the Wii U is coming out.

But, I don't think Sony will really push graphics as much as they did with the PS3. It just does not seem practical, or even lilkely for that matter! Don't get yourself too hyped for next-gen, you may get dissapointed.

The PS Vita is the closest thing to proof we have that the PS4 will be a powerhouse.

I'd have to predict a starting price of $450 with bleeding edge power. Sony will use modified off the shelf components to keep costs down and keep it cheap. They will make a very small profit on each system sold. BC will be a "coming soon" feature through emulation.

Hopefully whatever specific components they go with are optimized for 3D.