Why can't GET support that process? You'd have the extra bytes of the content, but there's nothing stopping the server sending the Link header in response to a GET request.
Yes, it's used a lot. If you look through web server logs, you'll see tons of cases where a search engine spider performs a HEAD, and then based on the headers, it decides whether the content has changed since last fetched. If so, it issues a GET.
Say you have a list of downloads, and you want to know how big they are. With HEAD and Content-Length, you can know, in a standard fashion, assuming the server tells you. Isn't this basic enough, that you'd want to put it in HTTP? What else would you do? Application-specific file-size queries? Doing a GET and then just closing the connection after headers? That's not pretty!
That makes sense. I was not challenging the inclusion of HEAD in the http verbs, just stating my own ignorance and hoping for illumination, which you and others and have now provided. I appreciate it.