We present a systematic comparison of data and theory for the statistical distribution of low-spin inertial parameters in normally deformed nuclei. In a comparison with 2145 measured yrast-band pairs in even-even nuclei, we find that the distributions in average absolute difference for both the kinematic moment of inertia ${\mathcal{J}}^{(1)}$ and the dynamical moment of inertia ${\mathcal{J}}^{(2)}$ are well reproduced by the projected shell model, but not by the usual cranking model with particle number projection. Some physical implications of these results are discussed.