This is why you might want a big sensor

Agreed

This ability is not a 'full frame' feature and not limited to any one brand.

Though perhaps sony should be given the most credit for their sensors. As I recall even their 12.4mp sensor in the Pentax K-x entry level camera could do this.

Mr. Dobson should get the Nikon if he likes Nikon, but it isn't totally unique to the D800.