My Suzuki has a slipper clutch, and believe me, it doesn’t make your shifts smooth. All it does is let the clutch slip when not slipping would cause you to lose rear-wheel traction or create instability during a particularly jerky shift. As you know if you’ve had the good fortune to use one, it’s plenty easy to shift like crap with a slipper clutch, which is why, I assume, you have your tongue planted so decidedly in your cheek. I guess the above was more for general information.
Seriously though, Rossi might be a bad example, but there’s a horde of motorcyclists who can shift as smoothly in the same manner.