Natural history enthusiast.
...Do all waterproof roof prism binoculars utilize these elastomeric seals in their focusing mechanisms? I suppose that's the only way to make something completely watertight...
The simple answer is no, or at least not comprehensively. In fact, many otherwise waterproof bins do nothing to keep liquids out of some parts of the focusing mechanism. An example, off the top of my head, is that in the original EL model (especially easy to see on later production), there is a conspicuous gap that can allow water or sand to enter, visible as a open slit along the top edge of the left side of the hinge, just in front of the focus knob.