Firstly I'll point out that mIRC never sends an MOTD request on connect, it's sent automatically by the server as specified in RFC 1459 (the original IRC specification). Raws 001 - 005 aren't defined in RFC 1459, their first mention AFAIK is RFC 2812 which, although mostly followed by modern IRC servers, is not necessarily required to be followed in order to be considered an IRC server. As a couple of people have already said, IRC servers don't process the information until after the MOTD anyway, and since by RFC 1459 servers must send either an MOTD or an 'MOTD missing' message, it makes sense that mIRC should use the most universally recognizable message that can be sent in order to determine the connection is ready.
