I don't remember this changing anytime recently... it's been that for at the very least a couple years. But anyway, I'll explain using a sample game between Zur, Kaalia, and Lazav.
Zur hits Kaalia's player. Kaalia now has 1 commander damage from Zur. Next turn, Lazav then hit her. She now has 1 commander damage from Zur and 3 from Lazav. Couple turns later, Lazav clones Zur's general and hits Kaalia with it. She takes zero commander damage from the fake Zur. Couple turns after that, Lazav steals Kaalia, pumps her a bunch with Hatred
so she's swinging for 18 damage. Kaalia now has 1 damage from Zur, 3 from Lazav, and 18 from her own commander. Next turn Lazav equips Batterskull
to Kaalia and hits Zur with her. Zur now has 6 commander damage from Kaalia. At no point in the above scenario does anybody lose or win via commander damage.
Actually, Uktabi_Kong and Kemev are practically the royal family of deck doctoring on this forum, and it's generally a good idea to listen to just about anything they have to say.
Deck DR Kong
1st Place in the Gabriel Angelfire Iron Chef EDH Competition
3rd Place in the Zedruu Iron Chef EDH Competition