  We comment on the article of Ch. Simon, V. Buzek and N. Gisin: ``No-Signaling
Condition and Quantum Dynamics'', Phys. Rev. Lett. 87 (2001) 170405, which
argues that linearity of quantum mechanics follows from lack of superluminal
signals and some usual hypotheses about measurements. We argue that such
assumptions in the end are ineffective as an explanation of the linearity of
quantum mechanics.
