Because Chrome for Android is in a pretty terrible state right now, and doing it on Chrome, it may have made it look even worse than iPad 4. Chrome for Android does a "good job" at making some of the most powerful chips on the market look pretty mediocre right now. I really resent Google for this right now, because they are embarrassing a lot of chips makers and device makers because of it. But whatever - they'll probably fix it in Android 5.0 (I hope).

So basically Tegra 4 shouldn't be "2x faster" than Nexus 10, but probably more like 1.5x-1.8x faster, depending on how much more they optimized the stock browser over Chrome.