The SME platter surface, Isodamp, is not new, just a different color. The manufacturer no longer makes the 'mustard' color used previously. Charcoal black is now SME's standard color, otherwise it is the same.
In comparing the 20/2 with the 20/3, the following can be noted:
1. The bearing's central damper has been improved, now more in line with the Model 30
2. the oil bath has been improved.
3. Weight went from 18.2 kg to 28.6kg - thicker chassis and subchassis; platter heavier and larger(from 4.6kg to 6.5kg and from 300mm to 312mm. (The Model 30 platter is 330mm in comparison).
SME wanted to narrow, not close, the gap between the 20 and 30 tables without eclipsing the value of the latter. The increased mass of the 20/3 provides much of that improvement.
I hope this clarifies the changes.