It's an interesting approach, and it's easy to see why they did it: Not only does it theoretically give the player more choice in where they want to play without rerolling a new character, it also prevents the nasty server queues that seem to accompany any popular MMOG. Champions won't ever have the problem where they need to transfer population from a shard filled to the brim to a shard that's more like a ghost gown.
Interesting and functional, certainly. But it's not MMOG-ish at all. The two key points, going back to that definition at the top, are the number of players and the persistent world, and Champions has neither. As far as players are concerned, the game might have hundreds of thousands of subscribers, but you'll only ever be with a hundred at the same time - tops. Most of the instanced locations don't have anywhere close to that. If you're playing in a Burning Sands with 60 other people, that's just barely twice the population of, say, a popular Team Fortress 2 server. That's hardly Massive at all - what good is having thousands upon thousands of subscribers if you only ever get to see a handful of them?
Nor does Champions necessarily pass the persistence test, either. This one's a bit trickier, though - as far as I can tell, individual zones are persistent. If I'm determined to always go back to Millennium City #27, I can, and it'll be the same Millennium City I know, always going on without me. But that's assuming that I manually pick every time. What if I just let the game shunt me into a zone it picks, one that might not be the same one I originally came from? It might be the same, but the people you play with won't - unless you have a cadre of friends devoted to a particular instance shard, your persistent world will never have a persistent playerbase.
So no, by this definition, Champions isn't an MMORPG ... but saying that sounds a bit absurd, don't you think? After all, the developers clearly intended for it to be an MMOG, just implemented in a way that circumvents some of the major problems of the genre. And in doing so, they may have inadvertently helped to blur the lines between what is and what is not a Massively Multiplayer game. By the strictest definition, Champions Online might not qualify as an MMOG, but maybe the problem isn't with the game - it's with the definition.
Where do we draw the line? Going back to Team Fortress 2 - it has empty servers and full 24/7 rounds on 2Fort, persistent worlds just like those in Champions, with a similar number of people. So yes, as Obi-Wan Kenobi might put it, even TF2 is an MMOG ... from a certain point of view, anyway. Hell, does there even need to be a line? Does it actually matter what we call a game, or does trying to fit games into niche labels just narrow our mindset?
Think about it, and get back to me when you can tell me when a stool becomes a chair.