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Nope. The reason the 13-inch got thinner is because it was previously thicker than the 15. So Apple reduced the thickness to match the 15.
 
According to Apple the 2012 Macbooks were 0.95 inch (2.41 cm), the both the new 12013 models are coming in at 0.71 inch (1.8cm). ALso the 15" seems to be 1lb lighter.

This is all confirmed at http://www.digitaltrends.com/computing/macbook-pro-2012-vs-macbook-pro-2013/

15'' weight is the same, there is no "1lb lighter". Why do I know this? The new Haswell 15'' Macbook Pro is 4.46 pounds versus the Dell XPS 15's 4.44 pounds. Dell is 0.02 lighter, but with the same machined aluminum with carbon fiber....
 
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