If by some bizarre event one or both of those clients gained a massive portion of the IRC user clientele then many servers would probably be forced to put restrictions on /who, either by ignoring more than x requests per user per hour, or even putting a vey low tolerance on what was considered 'flooding' when using /who. They might even have to limit the number of people using those particular clients, perhaps block them entirely. Ultimately this would mean that those clients would either have to drop or severely limit support of this feature to being practically useless, or otherwise face their users being banned from the majority of IRC servers.
