I think I've got something here. A couple of weeks ago on GoNintendo there was a write-up about how un-original most of the Brawl levels were. AKA they were flat with 3 platforms for the most part. And thinking back to Mario Kart DS you only got part of the tracks online (why I don't know).
But it seems to me that the abundance of these platforms will lead to not all of these levels being online. More specifically the generic ones we've seen. I think we'll see half of them (however many there are) as well as the more unique ones to save on server space. It will be disappointing not to be able to play on some levels online but seeing as how they're the same level, it would make sense.
Even with level hazards, I doubt there would be any need to have every level online. But, I still think we'll get 20-25 levels online, out of the 40 I've heard. I've also heard 40 characters will be in the game (we know about a third of them now with Mario, Link, Pikachu, Kirby, Samus (ZS Samus), Pit, Meta Knight, Ike, Zelda, Bowser, Yoshi, DK, Wario, Sheik and Ganondorf; so 14). In Melee we got 25 levels and 25 characters. So, an even setting would make sense.
But back to online. Would you really care about not having 6-7 level copies online? I wouldn't. I just want the unique stuff online. But, it'd be even more awesome if all levels were online. But, I'm just saying don't expect it.