The web is full of non-commercial sites — the ones that concern me are mostly academic — that do not necessarily have skilled webmasters in charge of them, so they're unlikely to be updatable to HTML5 or whatever, but are important to some of us.
While transcoding old "legacy" content might be a pain, all web sites would be equally easy to update. In fact, the HTML5 code for the web page you cited would probably take up less space, be simpler to understand, and support all of the latest versions of the most popular browsers (e.g., Safari, I.E., Chrome, Firefox, Opera, etc.) without any additional coding.
I am happy if Apple wants its browser to put up a warning before loading such sites. I am not happy for Apple or Google to decide on my behalf that I should be unable to view them because they think it's a security risk for my computer.
Media compression formats, along with web browsers and media players that display such content, are in a constant state of evolution. If the web site that carries the content you wish to watch elects not to evolve in a similar manner and/or be unsupported by the five most commonly used browsers, then it should also share the "blame." IMHO, it would be paranoid to think all of the browser manufacturers are deliberately crippling their products just to prevent a selected number of web sites from displaying their content. Isn't it more rational to think that these web sites are simply a bit late or no longer interested in keeping their pages up to date.
BTW, you do realize that this site represents an online multimedia resource originally created in 2003, none of the web site files have been updated (i.e., re-saved to the server) since 2013, and the server for the Rice University resources was non-responsive to the original URL when I attempted to use it. In short, it appears the original web site may have been reconstituted on a different server under the auspices or financial support of the National Science Foundation's Division of Undergraduate Education which may or may not be ensuring any "proper" continuity of the site and its content—i.e., the site is still programmed to handle connection by Modem (video or sound only options) and does not appear to have ever been "modernized" once it was up and running. The site seems like an "orphan" for whom no one wishes to claim responsibility.