Because you can run a maggy fine on v mounts, that's the way it was for about 8 years, and you can run a v with out using silly flexy ugly adapters which are ultimately still bolted on by the same flimsy pathetic m5 bolts.....Think alot of young kids have never seen brake bosses and assume they're v only. Who knows why it's different on both frames, but i'd say the justice will attract those more likely to use a 6 inch wide rim and no rear v. I personally hate 4 bolt so it's all good, if you want a magura on it, use the normal mounts you get when you buy the brake. Shame about the forks though, how many people actually use a front magura compare to front v users? Again seems a bit silly Leon