The polyphony counts for arranger keyboards. The Kurzweil sounds are indeed very good, and for a solo instrument they will work great. However, having 128 voices of polyphony gives the user a choice to use 16 notes of a rich sound, layered 8-voices deep, or 32 voices of not-so rich sound, layered 4 voices deep, or 64 voices of not quite-rich-but-still-very-good sounds. With high polyphony count, you, the user have a coice of either one, or the mixture of sounds. Moreover, in an arranger environment, a typical style will support up to 8 accompaniment parts, several of them polyphonic, each using up voices at the same time as you, the performer, are busy pressing the keys. Add to that the ability to layer 3 voices, even high-quality ones, in the right-hand part in a typical high-end Yamaha, and the fact that many sweet voices are using up to 8-voice layering, and you can very quickly reach the 128 notes of polyphony, even without pressing the sustain pedal.

Call me greedy, but I hope that the new crop of arrangers offers more than 128 voices of polyphony. IMHO, 24 voices is definitely not enough for an arranger.