Agreed. I was definitely taught to always shoulder check before turning right, and I can't remember whether I was explicitly taught or not, but it just seems like common sense to check if anything is coming before swinging your door open. That said, clearly it's not, so that really needs to be taught better as well. (And of course the third one that they do far better than us in Holland, and in Europe in general, is lane use.)
Each of these is clearly a matter of poor education. I still remember my driving test having three increasingly ridiculous questions about how it's never ok to go even 1kph over the speed limit, but no emphasis whatsoever on these issues. I hope it's changed since then, but the evidence suggests otherwise.