I supposed that Yamaha could do that because they can. I mean they know that they are the best or at lease one of the best in the business when it comes to arranger keyboards based on sales and user reviews so they can afford to make a new arranger with only adding one or two new features from the previous one. I.e. psr 2000-psr2100 and now probably Tyros and Tyros2.

BTW regarding 76 keys and having most if not all the features in one keyboard, I would not be surprised if Yamaha in their next flagship workstation incorporate a more software based system. It would probably have most things like the Motif keyboard, VST use and support and arranger features. The user would probably be able to work easily between the keyboard and a computer. They would probably have it in 61, 76 and 88 keys and most importantly they would have it priced to where most pro musicians can and would buy it.

To me, it is only inevitable given their competition like Korg and Mediastation to name a few. Yamaha is probably in the best position to make such a keyboard at a reasonable price given their market sheer, huge customer loyalty and their recent acquisition of VST.