http://www.classicfm.com/composers/mozart/mozart-piano/

Much of his talk following the performance is how composers wrote specifically for their instruments, such as Mozart for his light-action, leather-covered hammer Walter piano; or Bach composing for certain organs for which he had access.  Levin's point being that certain music just sounds better on the instruments for which it has been written, played in the style that the composer intended.  My friend who forwarded the clip to me remarked on Levin's style of play, which is much lighter, quicker, and wrist-and-hand-driven, as compared to that of many contemporary pianists, who drive pianos from the shoulders on down.

As Pianoteq represents both the contemporary and the old, it's an interesting explanation on why a stiff upright just doesn't play like a 1700s pianoforte - kind of like driving a truck through an autocross gymkhana course, just because it too has a throttle and steering wheel.  :-D