Actually, the RSX WAS NOT built specifically for the Cell. Now you're just making shit up.
The original PS3 had TWO Cell chips but for various reasons (cost being a huge one), that was scrapped mid-design. To quickly patch things up and get a working product, Sony contacted Nvidia and used an almost off-the-shelf design for the RSX chip. It was nearly an eleventh-hour decision.
The 360s chip, on the other hand, is a design made specifically for Microsoft. Not that I'm saying its a better chip (though it very well could be), but it's obvious that PS3 has a little more processing power (though I'm hearing that devs have turned to using SPUs to complement the RSX, which makes me question how well that chip is really integrated into the system).
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