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As demonstrated by Planetarion (wikipedia link), Dominion and various other similar games where your planet, kingdom etc. is represented by a webpage(s) of numbers and stats. These games have everything they need to be called an MMO and the ones which have player characters in them (instead of planets or dominions) are fully fledged MMORPGs.
A lack of a world does not unmake an MMORPG and a "true MMORPG" (if you insist such a thing exists) does not need a world nor does it need to be a world simulation.
I skate to where the puck is going to be, not where it has been -Wayne Gretzky