  It has been suggested that the observed $D_s - D^0$ lifetime difference can
be `understood' as due to $SU(3)_{Fl}$ breaking in the phase spaces for the
exclusive $D^0$ and $D_s$ channels `removing' the need for weak annihilation.
It is pointed out that several of the statements in this argument are
misleading or even inconsistent with a state-of-the-art description of heavy
flavour decays based on the operator product expansion.
