I wondered the same thing when I first saw that '13 seat just because it looks softer based on the outside material used. In the back of my mind I've also been wondering about finding and buying a used stock seat someone changed out to experiment with, adding a bit more foam and different outside materials like the '13 seat.
For now, if I know I'm going to ride 100+ miles in a day on the FZ8, I wear a pair of Fox MX gel padded shorts that I normally use when riding my dirt bikes. It does help some. Last week during vacation to MotoGP, we rode 367 miles the first day on the trip. Both of us on FZ8s were really feeling the seats. The '12 seat does break some after use, but its definitely not made for longer rides. I'm interesting in hearing what others have tried versus replacing the seat with an aftermarket one.