I've also read that only the RX-V1400/HTR-5790 and above have the Parametric equalization incorporated into YPAO. Another forum claimed that after contacting Yamaha, they were told that the YPAO features were the same and that the write-ups in the product literature were the only difference.
I only have the RX-V1400 and haven't seen any of the other units, so I can't tell you for certain. Still, the auto calibration, is better than nothing I suppose.

Personally, I'd be a little disappointed by Yamaha if this is true. They are implying that YPAO is the same across all the RX-V and HTR lines. This is the kind of marketing tactic I'd expect from a few other companies...no names. I guess business is business.