It's only better if you -- by reading up on convention beforehand -- know which way an edge points; does decreasing thickness indicate an incident node, or the opposite? Not clear on its own.
For example, (A -> B) is drawn:
A @===---- BActually, if I'm reading the paper properly, no it's not. The authors appear to have found that both the light-to-dark and the dark-to-light styles performed significantly better than arrows, and that the tapering effect was better still.
This seems reasonable to me: even if you're unsure about the convention at first, you probably only have to find one obvious edge to establish which way things "point".