Chakster, We don't "need" anything, but it is in the nature of audiophiles to believe that we can improve upon what the factory (any factory) made for us by spending money on a fancy substitute or building our own. This is not always borne out in actual practice, of course, but we audiophiles have the additional privilege of relying upon only our own opinion to determine success or failure.
Also, for every SP10 Mk2 or Mk3, there is not necessarily a factory-made obsidian plinth to be found at a reasonable price, if there is one to be found at all. So there is no shortage of aftermarket entrepreneurs to satisfy the need thus generated. I, for one, am very happy with the 80-lb slate and wood plinth I had made for my Mk3, and I spent less than $700 to get there. In my dreams, I would have wanted to remove the Mk3 motor assembly from its chassis and mounted that into the slate directly. But it's too late for that now.
Also, for every SP10 Mk2 or Mk3, there is not necessarily a factory-made obsidian plinth to be found at a reasonable price, if there is one to be found at all. So there is no shortage of aftermarket entrepreneurs to satisfy the need thus generated. I, for one, am very happy with the 80-lb slate and wood plinth I had made for my Mk3, and I spent less than $700 to get there. In my dreams, I would have wanted to remove the Mk3 motor assembly from its chassis and mounted that into the slate directly. But it's too late for that now.