Talk Fantasy Football

anyone know how they get the effect of the white stripes wearing off to show the blue underneath?

They paint thin lines of the blue onto the white. Example here. Starts at 1:17.

thanks for the link!

Although that's obviously an official GW tutorial, I suspect that the zug model may have actually been done with the 'hairspray' technique - that video actually uses a chipping medium and gives a more realistic chipping effect than you can probably manage repainting the base coat.
A word of warning: hairspray can be tricky and not great for game miniatures as paint can keep chipping.