We argue that the large Jahn-Teller (JT) distortions in YVO_3 and LaVO_3 should suppress the quantum orbital fluctuation. The unusual magnetic properties can be well explained based on LDA+U calculations using experimental structures, in terms of the JT orbital. The observed splitting of the spin-wave dispersions for YVO_3 in C-type antiferromagnetic state is attributed to the inequivalent VO_2 layers in the crystal structure, instead of the "orbital Peierls state". Alternative stacking of

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... ane exchange couplings produces the c-axis spin-wave splitting, thus the spin system is highly three dimensional rather than quasi-one-dimensional. Similar splitting is also predicted for LaVO_3, although it is weak.