Why is holding a joycon behind your back some test for reviewing the hardware?
Nobody plays like that.
One of the biggest selling points about the JoyCon is the fact that you can play with them separated. While I don't expect people to play with their hands constantly behind their backs, if the signal gets easily disrupted then it can be a problem for those who might be sitting in more relaxed/comforted positions that don't have a clear line to the system.