The assumption that a zero-incidence flow around bodies of revolution is axisymmetric has been broadly adopted by many researchers, even for cases where the flow around such bodies becomes unstable. In this study, the validity of this assumption is revisited using CFD simulation. As a case study, the simulations of both stable and unstable hypersonic flows around spiked blunt bodies in 2D axisymmetric and full 3D computational domains are compared. It is found that, for the stable flow cases, the main flow features are apparently axisymmetric and the assumption is generally acceptable. However, some degree of asymmetry can be observed inside the shear layer in the separated region, causing small variation in the drag coefficient. For the unstable flow cases, the asymmetry of the flow features is much more significant. More importantly, the assumption that the flow is axisymmetric is found to overestimate the level of flow unsteadiness. The amplitude of temporal drag variation as predicted by the axisymmetric solution is higher than that predicted by the full 3D solution.