Many jokes have a kernel of truth, and that's the kernel behind this classic engineer joke [1].
[1] https://www.et.byu.edu/~tom/jokes/Consultant_Engineer.html
Having that experience outside the company doesn't magically make it inaccessible, it just means they have to pay a fair rate, along with everyone else, for access to it.
What it allows is them _monopolizing_ those networks and knowledge and ensuring no one else can access it.
This is not a good outcome.
[1] http://www.smithsonianmag.com/history/charles-proteus-steinm...
I think this tactic is nothing more than deception, the guys are not staying around and give some guidance, they left or did not do the job the shareholders thought they were doing.
I have no problem, that people get payed big money to stay at the company and just to little consulting, but hiding their real position or amount of work is just theatre.