The problem with relying on ERs to be the sole hosts in the zone comes down to experience and numbers. An ER who hosts regularly will be promoted, and, under the proposed system, won't have to host anymore. Thus, a new ER would have to be hired, retrained, and thus, the cycle continues. What we eventually end up with is a constant inflow of ERs and a huge base of mods who do nothing but sit in spec and answer the occasional ?cheater. To add more experience to the entire hosting team and to ensure mods actually serve some purpose (excepting the few ?cheater and ?help messages we get, which, frankly, could be dealt with by no more than 2 or 3 mods), mods are made to host. Think of ER as a 'probation' period wherein one learns the skills to host, and moderator as actually applying those skills.