Although I do agree with the most part You said, Diki, the above statement doesn't make a much of sense.

First of all an arranger keyboard is not an instrument, actually it's lot more than (one) instrument, whole orchestra (and even more).

The purpose of an arranger keyboard is to mimic the sound of many different instruments (and majority of them is not played by keys), and to mimic the performance of the whole band just by chords and buttons, and it's not an easy task to accomplish.

Horn player (or any other instrument player) doesn't have to improve his instrument in that way because his instrument already sound exactly as it is supposed to sound. This doesn't apply to the arranger because, for instance, sound of the guitar played on a keyboard from couple years ago, and the sound of the same instrument from todays arrangers (namely SA voices from Yamaha concerning the sound) are quite different (almost incomparable). So the quality of the sound is improving over the years, along with the controlling options for the sound not played with keys (velocity sensitive patches, guitar modes, ...)

The fact is that not even the most advanced keyboards of today don't have the most realistic sounds in all "departments", or "top of the line" styles, or any additional characteristics that would made an "ideal arranger keyboard", so You have to admit there is still lots of space (for manufacturers) to improve.

Of course, all the above said doesn't excuse anybody who don't take time to get to know his arranger keyboard deeply, and instead using all the capabilities of that arranger, buys new model to sound more convincing with less of knowledge.

The true is, good arranger player will always perform much better on an older arranger, then lousy player on the "top of the line" arranger model.

P.S. Everything written above is just my personal view of the matter discussed.