And the moral is....
That platter size doesnt matter a jot, only performance statistics.
Who cares how big the platter sizes are? it doesnt make any different at all, as you never see them or have to accommodate them. They are built into the form factor of the drive and for all i care , the case could be 99% empty as long as the drive performs as promised.
Have you ever looked inside a midi system? there is nothing inside..... but they still made them that way because people want a certain size of product. As PCs have 3.5 inch bays, thats how big the HDD cases are, but the guts dont need to adhere to that size.
It's all irrelevent anyway as we will all soon be using some more modern technology that the venerable spinning media. Hell, there is probably some "magic" drive hanging about seagate or hitachi, but they want to offload their old fashioned magnetic media for another few years yet!