The document also forgets that API's are not read-only. So let's say you have users and usergroups and you can request a usergroup with its list of users and you can add users to usergroups.
If you use links for read, you should also use them for writes, otherwise it's quite inconsistent. So now you need to add a lot of parsing everywhere to extract the id's out of the urls, just for the sake of being more dogmatic