Glad I did a quick search before posting.
Yes, it would be nice if mIRC supported it's own protocol identifier (irc://) along with telnet:// gopher:// and all the others... shouldn't be too hard to just get the associations from the OS like any other program.
What I'd like to see is full use of the URL qualifiers such as <a href="irc://username:password@hostname.ext/channel?command=parameter" target="_blank">irc://username:password@hostname.ext/channel?command=parameter</a> and the like.