Yes, the lone 60 Rogue ganking questgivers in the Crossroads *might* be more of a problem. However, questgivers have short respawn timers and this kind of thing goes on at present anyway, and the response is generally a few Horde 60s flying in and ganking the griefer.
The other side of DKs was that it severely discouraged *genuine* "World PvP" - as in, attacks on capital cities and racial leaders. These are generally great fun for all involved, attacking and defending, and can be avoided by those just not interested. But the DKs for killing civilians were a major disincentive for people to take part in an attack. It completely prevents AoE attacks, for a start, and not to mention some of the civilians being really weak things likely to collapse if you breathe on them.
I could be wrong, but I think with the new honour system, Arena combat and new content on the way, the removal of DKs will only have a tiny effect.
The genuine griefer out to cause misery for others won't have cared about DKs in any case - and AFAICR none of the questgivers are tagged as civilan anyway.