To add to what Scott already said, I will make a couple of examples, drawn from my own experience with my Tyros 2:

1- The SA Saxophone not only has a soft and hard samples, but has also a legato sample, that plays when you play two notes in a legato way; this way of playing adds also a noise, made by the fingers touching the "frets" of the saxophone, to close or open the "holes" (sorry, I cannot find better words to describe this). This mechanic noise has nothing to do with the breath noise referred to by Scott.

2- The SA Acoustic Guitar has not only soft and hard samples, but also a fret noise that plays depending on the notes you play; specifically, I have noticed that it plays only after the last one of a series of notes, meaning that it does not play if you play notes in a succession, but only if you leave enough "dead space" after one note, just like a real guitar would.

These are just two examples, but -believe me- the Tyros 2 is a big step forward towards realism and my guess is that the same SA voices will be implemented in the next generation of Motif and will serve as a reference point for other keyboard manufacturers.