I don't think that's true at all. If you watch our video or read the article, taming resonances inside cabinets has long been a goal for many/most designers. Put drivers in a cabinet with no concern for resonances inside and see what happens to the soundwaves outside.
As Jack said in the video, usually it's with soft material, but a more targeted approach is what B&W did in the Nautilus with the tapered tubes and carried on with. It was a Laurence Dickie idea that has continued through his newer Vivid Audio speakers. The result of unchecked resonances translates into the acoustic -- and can be seen quite readily in the frequency response.
That said, KEF came up with a clever way to deal with it -- apparently VERY effectively.
Doug Schneider
SoundStage!