Tony, What I meant was that in direct-drive turntables, the motor, the drive system (aka servo), and the platter together form a closed system. So indeed the mass of the platter has everything to do with it. If you don't see what I mean, try removing the platter from a direct-drive turntable. The result will be a pronounced herky-jerky motion as the servo goes searching for its proper load. If you dramatically increase the mass of the platter (yes, "m"), the servo can get similarly screwy, slow to correct for off-speed moments, but it is less easy to see. It is the servo that tells the motor "how much acceleration is enough" to get back to equilibrium.
None of this is to contradict what you say about LPs with off-center holes (i.e., most of them). That's a big, important, and separate issue.