It's just different expected behavior. Drivers have to constantly be on alert of people doing their thing. Tuktuk rides in Bangkok can be exhilarating because of motorbikes crisscrossing through traffic right and left of you. I was glad our driver was used to it and that I didn't quite see a lot because of the low roof... Vehicular accident statistics are the ultimate judge here.
I don't know how Vietnam makes it work; they either have really alert drivers, really slow drivers or a really high child mortality rate.