Basically Nvidia took the entire display pipeline and put it on an external component.
The interesting bit is that the G80 is already huge, 480mm2 or so, a little bigger than the R600. Once you add in the necessary 50mm2 or so of the I/O chip, that brings the total to 530mm2, notably larger than the R600. For comparison the G71 is 197mm2 including I/O, so this one is almost triple the size.
