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We calculated surface displacements produced by a synthetic megathrust earthquake using two spherical, layered, elastic dislocation models which differ only in that one model accounts for the coupling between elasticity and gravity and the other does not. We show that including gravity perturbs the displacement field differently in the near-, medium-, and far-fields. As a result, slip inversions based on an Earth model without gravity cannot simultaneously fit the near-, medium- and far-field displacements generated using a forward model including gravity. This suggests that the spatially systematic misfits between observations and dislocation predictions seen in the literature arise, at least in part, because these studies are based on models that neglect gravity. Although the magnitude of the far-field displacements is small compared to those of the near-field, our slip inversions show the most improvement when we both up-weight the far-field observations and use a physically consistent model in the inversion.