The enormity of the consequences of HTML only allowing GET and POST cannot be overstated IMO. It's maybe the most damaging technical decision in the web standards space - ever. I see HTML forms as a root cause for the WS-* "everything goes over POST" debacle, a billion dollar industry mistake, at best.
I've always wondered what's the history behing the GET/POST only restriction in HTML. Was there a good reason (or did something appear to be good reason) for doing so? I can't think of one.