Most of the time I thought of the mission and such waits to be more a way to battle against congestion at NPCs and battlefields and whathaveyous.

Of course this would only really make sense when the missions and quests are very new, and should have been lowered or removed later on.

The time-sink reasoning is much more likely to be true, but I still rather think that's not entirely the case... even if it's just to fool myself a little.