Actually the difference is the piano based arrangers have more than five octaves...the one's that aren't piano based, the "normal ones", as you put it, have 61 keys.

From Yamaha's NP-V80 description...

"In both design and playability, Yamaha's piaggero embodies the almost lyrical combination of "piano" and "leggero" - Italian for "light" - that constitutes its name. NP-V80 is upper model of NP-V60.

Graded Soft Touch Keyboard just as on an actual piano with soft touch of digital keyboard."

The instrument is based on a digital piano...the NP-30. It has 76 lightweight graded keys.

No "normal" arrangers I know of have graded keys, only the piano based ones have them.

The instrument in question, the NP-V80, was designed for those wanting a lightweight digital piano with some arranger features.

Now, let's see...anyone buying a Roland arranger, cannot upgrade to 76 keys...they only have the Prelude/GW-8 arrangers.

If 76 notes were as popular in a higher end arranger as you say, why didn't Roland continue to give their customers a choice of 76 keys when upgrading?

Roland has no 76 note upgraded versions of the Prelude/GW-8 available, yet you seem to feel that Yamaha should make a 76-note PSR-S-series.

So, how come, if the market is so lucrative, neither Roland or Yamaha wants to provide an instrument to fill it?

And you thought I was grasping at straws...you've got your head in a haystack.

Ian