We also get the round head type cabbages - Brassica oleracea. In Chinese, these are referred to as 包菜 (Mand: bāo cài; Cant: baau1 coi3) , with bao meaning wrap or bag.
One slight variation is the one known as 京包菜 (Mand: jīng bāo cà; Cant: qing1 baau1 coi3) , where jing/qing is an abbreviation for Beijing, so Beijing cabbage.
No. I can't see much difference either.