The line has to be drawn somewhere. Why not 50? Joining a room with a name like #ThisIsARoomWithAReallyLongNameBecauseILikeLongNamesAndItShouldBeIncludedInmIRCRegardlessOfWhetherPeopleCareForItOrNot is a bit silly if nothing else. As for the nickname issue most servers support lick lengths of around 30 chars or so these days, that is also a reasonable limit.
If mIRC did come to support 200 characters then someone would come along and demand it go even higher, again it seems pointless to me. I'd prefer development efforts to be put into something more useful.