I thought this was very informative. He was obviously cover just the big US four in his comments which is, in my opinion, a very reasonable way to go about a conversation such as this. If he were to include the European manufacturers and the more esoteric US manufacturers, a tidy nine minute video could easily become twice as long. He has to work within the format of the online show that is shooting this.
As to his "die cast" comment, I am quite sure he is aware that die cast is a manufacturing process and not a metal in and of itself. I do a lot of presentations for my job and they are mostly voice overs, very much done in a relaxed, conversational style. I quickly found that it was far quicker to write a script and read it then it was to just talk about the subject off the top of my head as I often made errors like the one mentioned. Let's roll a camera or two and let one of us start talking vintage drums and you will be amazed at the things you will hear yourself say.
Pretty cool information. His presentation would tend to make you feel like Rogers was the cream of the crop in the day and he explained why this was. Of course that is all subjective but still a very interesting observation and it has been echoed by many here. If one were to believe that line of reasoning (and again i understand this is entirely subjective) it brings some clarity as to why current manufacturers typically utilize sharper bearing edges. from his commentary it is simply the process of furthering the state of the art.
By the way, did Slingerland per apply their acetate finishes to the plys and then wrap that into the scarf joint as well? I should know that but I am pretty sure I do not.