Combat in MMORPGs, along with loot, stats, levels, experience points and powers are all what used to be counted as 'wargame mechanics' in the early days of RPGs (though, paradoxically, these days the industry refers to the same elements as RPG mechanics). Driven by numbers -- the one thing a computer does really well -- numbers are easy to automate and adjudicate, requiring no understanding or judgment. An ideal task for a computer.
But strip away the combat from many modern MMOGs and there's still potentially a lot left. Despite the barriers, there are still role-players. There's socializing and crafting mechanics, games with musical performances and mini-games. Some say EVE Online could be handled without combat -- and some of us talk fondly about the idea of a Rock Band MMOG or a Singstar MMOG. Star Trek has been put forward as a setting where combat could be marginalized or nearly eliminated as a character activity, and of course there's the successful Egyptian MMOG, A Tale in the Desert -- now in its third incarnation, and entirely focused on non-combat activities.
Would you consider an MMOG without combat? Can you even imagine one being popular -- or is combat the core mechanic around which all big-time MMOGs must inevitably revolve?