I'm not quite sure I understand. Do Americans not look at what's coming from behind them before opening a slab of metal and glass a meter out the side of their cars? Kind of reminds me of when I first moved to Thailand. My (now) mother-in-law asked her daughter why I kept looking over my shoulder when driving her car, and why/if I couldn't use the side mirrors. She had literally never heard of nor understood the conc…
I've done a good amount of driving in the undeveloped and developing world (40k miles AK->Argentina, now 10k miles in West Africa, going to do about 80k)
Blindspots are not considered here. Driving is much more fluid, and you really only need to watch what is happening in front of you. After all, the car behind/beside you can see you much better than you can he, so just move over and he'll get out of the way.
If you're going to do something really strange (stop in the middle of the road, turn where you shouldn't, back out into flowing traffic) you just tap your horn and go ahead and do it. Everyone else is paying attention and will flow around you.
It really is a different way of thinking, and it's immensely impressive that everyone is paying enough attention to make it work really well (Traffic accidents are not common, and the driving conditions are so, so much more hectic than the developed world.)