The attractive Hubbard model is used extensively to model conventional superconductivity. Whereas in the strong coupling limit it reduces to an XY model, the intermediate coupling region displays a curious dome-like dependence of the critical temperature (Tc) on the coupling strength. We compare numerically both sides of the Hubbard Tc dome with the equivalent XY model and draw conclusions regarding the mechanism by which superconductivity is lost, with possible implications on cuprate physics.