It is a different type of durability. Neither is a growth of aluminium oxide from the metal substrate like Type III "Hard" Anodisation.
I understand that SureFire experimented with trying to achieve yellow in type II and were not satisfied with the available shades of yellow, nor the consistency of the shade/hue.
They compared the physical performance characteristics of coloured anodisation with those of powder-coating and decided that the powder-coat was the more suitable finish to go for.