When you hear a piano, you'll hear the upper strings to the right of you more (if your playing it) and the lower to the left, thats partly what its for. Stereo generally gives a more live and natural sound though, at college we mic them up in stereo, and the channels are panned on the computer afterwards, the difference is quite noticeable and its definately an improvement. Also, a single mic might have difficulty picking up all the strings with equal dynamics, to do so it would need to be placed at some distance from the instrument, which generaly negatively effects the sound (depending on the application, for classical recordings, the piano is a long way away from the mics, and its fine for that use, but with a heavy backing track, it will not cut through well at all). Again though, doing it like that requires 2 mics as reverbs don't make much sense to our ears in mono, and reverb is what you'll gain, though in a normal sized house I doubt there is much to be had.
I'd actually be worried about owning something like that which is so expensive :shock: . I bet there are people out there that claim the gold plating improves the sound :lol: