1.) You can not compare the car industry with a keyboard producer
2.) Does Korg, Roland or Yamaha the same - no, they do not
and that's relevant because?
I do get your point and agree in some respects, Hammond always did the same as Ketron and it caused some problems amongst the retired home users. However the proline instruments (the new B3 and XK series for example) caused significant interest and by the time the products were ready it was very easy to sell them from release. It also stopped customers who were thinking of a change jumping ship
Ketron, like Hammond, are primarily supplying instruments for the pro market. Current MidJay owners are not unhappy with their instruments but now have time to think about what might be their next equipment and how they could fit the new technology into their setups. Ketron have the time to adapt it as requests and ideas come in.
But there is no wrong or right way of proceeding, it obviously works for Ketron as they have been doing this for years, and ok, it might cause annoyance among a handful of customers (particuarly this very odd corner of the internet that is the Synthzone arranger forum), but by the time new products hit the market everyone will know about them with very little effort on Ketron's part.