Here's my thought:
Yamaha was disappointed at the consumer response to the Genos (in terms of sales), and since the technology was already built, and tested, they decided to capitalize on it, and put it into a more affordable package. If I'm right - smart move. Put the better technology into more hands. (under more hands?)
Remember the early days of Technics kbs? There was no published list price, and only dedicated piano stores sold them, so they charged whatever the market would bear. Today's consumers are better informed, and so, the market has shifted in favor of the buyer.
These improvements to the PSR line will certainly interest more buyers who, like myself, have avoided the product for many years. My gripe has always been the key feel. If that's truly improved, then I'll be happy to add the SX to my arsenal.