I think it is an oversight: Box isn't particularly special with how it handles ownership, but people do get the wrong impression that Box is the way to have uniquely owned data, whereas it is actually the default. This happens less now that Box doesn't have special syntax, but I agree with you that we may be able to improve those docs in this respect.

Unfortunately, it can be hard to have an example that's simple enough to understand, while still emphasising the right concepts. Hopefully we can find something.