I have never run out of polyphony on the Tyros4 and I use layered sounds and custom styles revoiced with lots of pads, mega-voices, and SA/SA2 sounds, especially for my Freestyle styles.

I guess it is possible, but so far, not a problem, even when using multi-layered RH and a LH sound.

Back in the old 64-note poly days (my old PSR-8000) it was an issue for sure, but as DonM says above, they seem to have got better at allocating voices.

Ian