Even if mIRC would /who all chans say every 5mins - and I assume it never will, as the slight gain in "useful once in a while" funcionality can in no way justify the additional constant load for all IRC networks
One could prevent that by providing the functionality and the interface but not activating the polling by default, but only on request. (e.g. a user-preference which offers to check for away-status and then activates it and/or when a script "registers" for that service)
there will always be some situation (or user) that - allegedly - requires a more up-to-date /who-result.
Manual /who-commands should not be disabled by that functionality of course.
Also note that various IRCd take various parameters for the /who command, so replies to custom /who-requests could complicate attempts to get a reliable "full poll" if mIRC would not opt to ignore all custom replies at the cost of even more overhead.
I have to admit I am not aware of the exact differences, but for now I would assume there is an intersection set most servers share which could be used in a useful manner.
