HTTP URLs and HTTP methods are two very different things, somewhat conflated in that the browser treats URLs in the URL bar as a shorthand for generating a GET. While URL encodings are well standardized for general use in RFCs the parsing into an HTTP GET when entered into the URL bar is not, it's just good UI. The same would be said about the QUERY method standard, it's not about describing how the browser UI should allow making such a request header just what a valid one is.
Just as a small remark, HTTP protocol standards do - or have at least - considered URL input so far in a wider, client-side meaning. Some details are left for the clients, e.g. it differs across browsers how certain URL characters are interpreted when entered into the URL bar (or on the command-line, e.g. with curl(1)).
Apart from that, HTTP URLs are part of the same HTTP standard, aren't they?