I believe there is truth in that. I think a lot of it is marketing driven. I still run DSM2, some stuff is using newer DSMX Rx but still DSM2 link. JR11X and 9303 Tx. I am a big fan of the 11X (now upgraded to XG11 software). I used DSM2 at IRCHA in 2011 and there were a lot of helis in the air! I have never had an issue. I have spoken about upgrading from DSM2 to DSMX on two occasions with Horizon Tech support since summer 2011. Both times I heard the same thing. The improvement in performance is difficult to measure, more theoretical than provable. And it was suggested both times that if I am happy with my DSM2 than maybe I should not worry about it...
Now that JR is going with another system I would also consider Futaba if/when I buy another radio. All of the Spectrum/JR equipment I own would be incompatible anyway. As for the DX18, I have programmed both airplanes and helis with it while helping others, but I don't know if Spectrum will ever produce a Tx with the fit, finish, or feel of a higher end JR or Futaba radio...
Disclaimer, I still fly IMAC and a few gliders on an old Futaba 72mHz radio, so I am usually slow to adopt new tech anyway, LOL.