The discussion on heat rings go way back. According to an ex-member, (I believe it was a Wagner catalog he quoted from), that Wagner called it a heat rim and that it was to allow the heat to spread out more evenly underneath the skillet to avoid "hot spots". That doesnt mean it wasn't intended as a leveling means on the older gatemarked cookware.
The notch on a Lodge Heat Ring was also discussed. Someone said Lodge created the notch to allow heat to escape, then added 2 more notches, but it was mainly a sales/marketing gimmick......but having escape notches sure blows the name "Smoke Ring" out of the water...... ;D