I collaborate as a grad student with my advisor and committee and lab group. We do not, however co-author all the same documents. We have similar processes of synthesis....so is that acknowledgement? co-authorship? or collaborator?
I think that ideas are intellectual property and if shared that is collaboration. Ideas deserve acknowledgement and if someone wrote something and asked for edits. It doesn't mean they wrote it....they edited it and deserve some sort of acknowledgement for that effort and recognition for ideas. Graduate school is a hazy place riddled with lack of understanding from clear definitions of these terms.