The Dumb----- at Yamaha marketing make sure they don't interfere with Genos sales....Actually they are missing the boat because putting aftertouch on a SX-900 would cost very little and make a lot of us happy. It would not cut into sales for Genos, IMHO.
Are you sure it would cost little?
The same decision has been made with MODX versus Montage, and other mid-range synths like FA-06/7 and Krome have no aftertouch either.
The midi parameter is always there, i.e. connecting a controller with aftertouch works.