Hi Donny

Having been in music retail for 30 years including owning a full line music store, they are from my experience saying there is a small amount of people who buy these products that would use 76 keys and that 61 keys fits the needs of the market they are going after. Space and weight may be considered, but not a real biggie I wouldn't think.

And, very possibly, they are concerned that if there is a 76 note Tyros that maybe they will loose sales of the very expensive Clavinova CVP series line.

I don't have a crystal ball or a direct line to Yamaha,but really what else could it be.