This is a quote I saw in another forum talking about this topic
Alternatively, some Monitor manufacturers have allegedly started to call 6-bit displays equipped with an 8-bit (or 9-bit) driver "8-bit". I hope that this isn't what Sony is doing. While these displays can dither better than other 6-bit displays, the end result is still dithered (physically or temporally).
And the only panels i've seen listed as 8 bit are 17 and above.. None of these are in the Macbook Pros (though it possibly could be in the matte 17" inch but unlikely)