Mr. Snrub said:
The machine has nothing to do with it. It has everything to do with Cobb having been to limbo/experimenting in it. Remember, they said that it's pure raw subconscious, unless one of the shared dreamers has been there before--in this case, Cobb had been there. It's feeding from Cobb's own subconscious and what they created there.
Yes, each person has their own limbo, but if they are all connected, then the dreamscapes are shared. As for neurally...I think you're looking too much into it.
If Ariadne enters it again alone, then I can only imagine Cobb's vision would have SOME sort of influence over what she thinks it is...but I don't know.