Sometimes there's a debate as to whether you are allowed to connect a dishwasher or garbage disposal using a flexible cord. No matter your position in that debate, I think you'll agree this guy is wrong...
The central vacuum at my mother's house has a SJT cordset, that had a section of 3/8 flex slipped over it to "protect" it. (it's in the garage, but I don't think it needed that level of protection..)