What makes for a "great" turntable?

I know that the cartridge, tonearm, phono pre-amp and other upstream components make records clearly sound different, but what is it about different turntables themselves (cartridge and tonearm excluded) that affects the sound? I would guess isolation from external vibrations and rotational accuracy. After this, what else is there that makes a great $30000 turntable sound better than say a much lower priced "good" table?

Also, how significant is the table itself to the resulting sound compared to the other things, ie tonearm, cartridge, phono pre-amp, etc?