actually the twin rear shock setup worked as well as the single shock setup did, however it weighed more and lifted the center of gravity which along with the exhaust caused handleing problems.
so they stuck with what worked.
ya they did, I really give yamaha kudo's for there development style tho, don't get to crazy trying 20 different things (a la aprilia) just stick to a small number of changes at a time, so you can actually tell what made what difference, as opposed to just guessing. scientific method, isolate the variable before you play with it.
makes for a more conservative bike, but it also means that it's easy to ride and easy to set-up. I don't think there's any doubt now that this approach has worked for them.