Physical quality control issues. There was a big problem a while back with Nvidia integrated graphics failing pretty often that apparently had to do with bad potting material material in the chip modules that didn't have the same thermal expansion properties as the solder that Nvidia had switched to. A large number of MacBooks had to be replaced, costing a lot of money and consumer confidence. Google "bumpgate" for more information.

And while Nvidia's Kal-El is really nifty, I'd rather have an OMAP 5 in a mobile device. Four A15s at 40nm will probably drain too much power to get any sort of battery life while playing that demo. 28nm should be much better.