There is a difference between what the CELL is able to process and what a general Intel processor (including Nahalem) can process.
The CELL is a media processor, its ability is to be able to process, decode, and encode the many forms of file types but it can also act as a GPU in terms of processing games graphically and texturally. The CELL is insanely fast at processing number equations needed to run many different AI streams at once.
A general CPU is stronger at general physics based tasks like Physics engines and running the code behind the scenes, this is why you need a GPU. The newer Core i7 processors fair better then the Core 2 against the CELL at crunching numbers for multiple streams.
I think this is as general as I can make it.. there really isnt much major difference between a general processor and the CELL other than how they are architecturally made to handle different tasks.