The trick is to make those 'timesinks', for lack of a better word, not only seem important, but also attach a sense of decision making, risk, and consequence to doing them (or not). Then they're no longer all that trivial. Blizzard is pretty terrible at this particular aspect of MMOs. In the examples you gave, flying to vendors and such have zero risk to them, and are, as such, completely uninteresting.
Rail against it all you like, but mmo's fall flat on their faces without these elements, and they always will.