The same question comes up, why would a DRK want less emn? In a zerg you'll have spikes on and the hate cap will be reached so fast emn reduction wont matter and chances are a DRK wont pull hate either way. In a longer fight DRK is a pretty solid tank and has access to great pdt mdt sets.
DS still has some uses, maybe arch DL and AV. You wont need it in Abyssea or on any other content. Maybe when they add more HNMs?
DE while not great can be used on any of the new content. Even if you use it once a week its more often then 99% of DRKs will be zerging arch DL or AV.
Dynamis is a great example. 9/10 mobs Acc will be just fine with good gear. Then you pop a NM and need Acc/att. You can rock pizza the whole run with the acc benefiting 10% of the time or rock RCB and pop DE when you need it.