I believe that instruments have been considered for ergonomics, to the point where it still can be what it is. To say otherwise is like saying all cars look the same because they all have 4 wheels. If you "rethink" a car too much, it's no longer a car but something else.
I'll take an instrument that I play myself - guitar. Acoustic guitars have a large body to provide enough reverb volume, but the shape is fit for placing it on your knee - ergonomics. Too say that an electric guitar is just an adaption of the acoustic is incorrect - the volume is greatly reduced, the neck is slimmer, the frets and strings are closer, neckstrap is standard.. all those are ergonomic adjustments that could be done because you got rid of the volume and could now play standing. A major change in form factor would require tampering with the string arrangement, which would make it a different instrument altogether.
And that people play whatever their idol played - a Les Paul or Stratocaster - is true, but not as simple as that. The two have different pickups (microphones) that produce very different sound. Humbucker on Les Paul that produces a beefier more distorted sound common in riff based rock, and Single Coil on Stratocaster that has a much cleaner sound favorable in solos. So you want to use the guitar same as your idol not only to live up to the image, but to play the same music, that you want to sound similar. Granted, your first guitar you won't know or care about those things and you won't know any other guitars than those 2, but your fist guitar won't be one of them anyway. When you can afford a Les Paul, you might go for an Epiphone, a Telecaster, or an ESP.
Also, the open-door-with-your-opposite-arm being teached in Sweden is probably false. At least that's nothing I remember from taking my exam 10+ years ago. Sounds like an anecdote someones teacher once said, but highly unlikely to be a routine. My teacher used to teach that "when you see a sign "Town_X 5" you should be in 5th gear because you are on the highway, which is complete gibberish for reasons I won't even bother to type. To open the door with your left arm is natural behavior when you open it to the left and cyclist should be in the bike lane anyway