We have investigated the mechanisms of lateral ordering of InAs/GaAs quantum dot superlattices. Using cross-sectional scanning tunneling microscopy, we determined the lateral spacing between dot columns in a series of five-period dot superlattices annealed for various times. As the annealing time is increased, the average column spacing increases, while the distribution of column spacings is broadened. A comparison with earlier studies of one-, five-, ten-, and twenty-period dot superlattices suggests that the lateral column spacing is determined by strain-enhanced bulk diffusion. We propose a conceptual model for self-ordering of quantum dot superlattices based upon a combination of island nucleation plus strain-enhanced island dissolution.