Since I have both I can agree with that statement.
I have notice that the sounds of the Yamaha are very good, but seem very thin, almost all of the Yamaha sounds in thier base form have at least 2 wavesamples layered, which would mean the Polyphony would be be half just by that comparison,
The Korg sounds are much fuller, In both defense I never had a Polyphony issue on the Korg or Yamaha.
So I don;t think the Polyphony really matters that much, I did have a problem with my SD1