Not even close. All Yamaha keyboards use a technic of sampling called AWM. However, the amount of sample Rom within each product and the type of "sound engine" that is used is very different from model to model. Once a company has sampled certain sounds, they may decide to use these samples over and over again in other products, but in lower priced PSR keyboards, the result might and usually will be very different from higher end pro keyboards because there are so many more parameters available to the sound designers in the EX or SY or Motif or S series keyboards than in the PSR550 vs PSR2000 keyboards. So, although AWM is used in all products, there is such varying degrees of how the finished sound will be based on what Engine was used to put these AWM sound bites to their full potential. I hope I have explained this ok. It's a question I myself raised to Yamaha some years ago when this question came up at my store.
George Kaye
Kaye's Music Scene
Reseda, California