@grofire And not all Fun games include progress.
Ultima Online, ,arguably the first major MMO to come out didn't really progress beyond a certain point, as @spoletta said, yet people came back for years and years, and there are still people playing the game today.
Another example is SecondLife. SecondLife is a social game in the same league as The Sims, but other than amassing some in-game wealth, there really isn't too much progression in it. Second Life is a beloved game, that is played by many groups still. IMVU is a clone of SecondLife, and so it is probably similar (don't know, didn't need a clone)
Think of games like Pokemon games, not the Gotta Catch'em All ones, what about Pokemon Safari. A HUGELY popular member of the Pokemon franchise, that didn't really have levels or anything. You just wanted to collect all the pokemon...and then, once you did, you kept playing for the joy of playing, no progression needed.
We're all in agreement that some small bit of vertical can be in the game. Equipment is giving verticalness to the game. Talents give some progress, but it needs to be kept small.
Yes, @spoletta also mentioned the fact that brand new players have the young status for a little bit to get some variety in their builds, which will help, but the fact of the matter is, the starting abilities aren't too bad for any of the builds, and they are still playing around with them and balancing them too. We have a different set now than we had before. Magic Missile is still one of the best spells to acquire, and you pick it up during the little introductory guide questing. This is like the tutorial getting you familiar, and you pick that up. Other builds get other skills that help round out their characters. Point is, you could still play the game for years with JUST the starting skills and still be a perfectly viable character. The different skills give you choices, AND the ability to customize for specific mobs/opponents, but otherwise, your pretty viable. Your example, @grofire is more of one of those Rock-Paper-Scissors cases, where the Fire Resistance would counter the main attack of the Fire Bolt player...but that player would also have a chance to get Magic Missile during their tutorial, which is easily covered during the young status, shoot, it is unlocked in the first 30 mins of play for most arcanists. You can also attack with the Primative Mage Staff, which is just Magic Damage, not Fire, Lightning, Poison, etc... and you learn to make that in the first 30 mins too, from very common stuff.