Earlier quoted context omitted.
The difference of Mendeley is that they had a good PR team, and composed of academic, "people like us". And they were everywhere, and this PR team banged on the note that Mendeley was going to be open and "grassroots" academic, because it was made by academics. Now, we know the real answer.
All those employees just turned into evil drones this week because of the acquisiton?
It means that a week ago CEO could make the same promises and be heard seriously, but the same CEO promises right now are not worth the paper they're not written on.
Now at any point in the future all the Mendeley 'openness' promises can be easily broken by Elsevier, so they either know that all the promises they're making now are empty (i.e., lying intentionally) or they don't know that (then they're naive and incompetent as general managers).
Promises can be made by those in control. Leaders in public companies can be considered in control. Leaders in privately held companies can be considered in control if their public vision and roadmap is aligned with the owner. But if the owner has a clear interest to change the roadmap - then it would be imprudent to rely on such a roadmap. Elsevier has a reputation of intentionally sabotaging projects (say, gov't initiatives) that should bring openness - if they fool you twice, shame on you.