Really? I've always seen it as a percentage of colors that can be displayed (sRGB). Of course, a graph would be better, but according to Dell, my U2410 has 110% color gamut and it looks pretty amazing to me.

As for the Retina, I may have to take that back. First article claims the Retina has 99% vs. 71% for the previous generation:

http://cdtobie.wordpress.com/2012/06/18/color-gamut-of-retin...

But Anandtech says it got worse (67%):

http://www.anandtech.com/show/6023/the-nextgen-macbook-pro-w...

I'm assuming calibration has something to do with it, or somebody tested it incorrectly or with inferior equipment.