You must be looking at different ultrabooks than I am then.
Thnk about it... The hardware and battery on an ultrabook are fit into the keyboard section. On a tablet all that needs to fit behind the screen. An ultrabook is usually set down on a table while in use. A tablet is usually supported in ones hands.
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The Pro is gonna be a bit thicker than the RT. They'll have as much room to dissipate heat as any ultrabook.
The problem is said heat will be dissipating into your palms. And the LCD for that matter.