By 2 camera,s I meant 2 lenses. 35mm is overrated. I mean, not everyone is Christopher Nolan who can still film on those films. Anyway, I think 3d camera in hollywood uses to lenses, and they use a mirror to bounce the second lense to not have too much of a perspective difference anymore. I can be wrong, However, I think it's normal to composite the 3d shots later because you can adjust manually the perspective of your 2 shots to get more depth in some things, and less in some other, so I think the whole digitally added thingy is necessary.
But yes, mostly cash grab. I mean, after the avatar hype, everyone was trying (and many failed) 3d movies. I mean, the hobbit in 3D was horrible and made people barf because there was just too much thing going on.
btw, have you looked to the TVs that convert 24 fps to a fake 60 fps ? It's horrible. It makes every hollywood movie fake as hell. It's quite an interesting thing to see.