yep... Though, in all fairness, you CAN potentially make a 58% DI weapon on SP, more if you craft one of the recipe items with additional DI as a recipe bonus.
It is actually more of a factor on SP than on other shards, due to the lack of insurance. Wear ex armor, and use your SP personal blessing on the weapon, and you will have an edge over those with pre-lore-bonus weapons, and non-runics in general.
On the other shards, DI is more useful for the PvM crowd, as what is a minor bonus for PvP is a major one against creatures, even if only at 5%. Against people, more DI from Arms lore only amounts to 2-4 more points of damage; against monsters, it can be 10 points or more. Add in Runic DI, and the difference gets closer to 10 more points for max DI (compared to exceptional non-runic) in PvP, 30-40 points difference in PvM.