Two of the same stage. Why? Just because of the size?
Yeah, that's what I mean.
Are we getting even more stages than those we can see in the picture I quoted?
Yep, Sakurai specified in today's Direct that Battlefield and Big Battlefield - the two stages you're talking about - are indeed separate stages. Big Battlefield is geared toward 8-player matches.
And yes, we definitely are getting more stages beyond what's listed there. We've known Pac-Land exists for a long time and it's not shown there, and from the Event Matches we saw in the Direct we know Pokémon Stadium 2 is in the game, and it's not there.
There's also no version of Flat Zone there, and I think we can safely assume Mr. Game & Watch will at least get Flat Zone or Flat Zone 2 back.
It's also very likely Magicant and Mute City SNES are in, as each major franchise seems to be getting at least two stages from what we've seen and
Mother and
F-Zero both only have one stage so far, and they're returning ones to boot. It makes too much sense for them to be in the game, Magicant especially because there's a Flying Man token in Smash Tour.