As an aside...I recently tried to purchase a Roland Fantom G7 from both Guitar Center and Sam Ash. Neither store stocks 76 key keyboards, they are special order. The only maintain stock of 61 or 88 key keyboards. The reason being most of the public will only buy a 61 or an 88 key.

So I don't think the argument is specific to Arranger keyboards and Yamaha, this seems to be an industry trend. That's probably why you won't see ANY 76 key arranger keyboards at a music store; let alone high priced arrangers like the Tyros 4; they are just to expensive to stock and / or they don't sell well.