  In this Comment we show that the temperature-dependent effective Hamiltonian
derived by Reslen {\it et al} [Europhys. Lett., {\bf 69} (2005) 8] or that one
by Liberti and Zaffino [arXiv:cond-mat/0503742] for the Dicke model cannot be
correct for any temperature. They both violate a rigorous result. The former is
correct only in the quantum (zero-temperature) limit while the last one only in
the classical (infinite temperature) limit. The fact that the Dicke model
belongs to the universality class of the infinitely coordinated
transverse-field XY model is known for more then 30 years.
