The Hyperspec is a copyrighted document owned by Lispworks. They can change it, and *perhaps *others could create a revised version under the generous terms of use.
But the Hyperspec is mostly a version of the official ANSI specification for CL, and revising *that *is something much more difficult. (I won't here go into the story how X3J13 manipulated the final draft of the ANS into a freely-available document prior to ANSI slapping their restrictive copyright on it, but that's what the Hyperspec and other similar freely-available versions of the CL specification are derived from.)
The erroneous example you found is real and it would certainly be nice to fix it, but note *1.4.3 Sections Not Formally Part Of This Standard. *Sections labeled *Examples *or *Notes *are not normative -- i.e., they are illustrative only and not a binding part of the language definition.