The TDP for a quad core Sandy Bridge is 45W over an area of about 1 CM². Imagine a 100 Watt lightbulb, how hot that is if you grabbed it with your hand, and how quickly it gets to that temperature. Now imagine if the heat from that was concentrated about 15 times from the surface area of a lightbulb down to the area of CPU die.
The TDP of the dual core Sandy Bridge chips is 35W. My cheaper soldering iron gets to 300C+ in about 1.5 minutes and is also 35W.
Its actually remarkable how controllable the temperature is in these laptops.