If the Mikes can be ousted from RIM, you can bet your rear that Hastings can be ousted from Netflix. And once "maximizing shareholder value" becomes the goal, "culture" becomes an afterthought.
Can't say I've ever heard of an organization where that's true. Typically, adequate performance means no promo, and being first in line for dismissal if the order comes down to cut staff.
Firing someone who is trying and doing sort of OK-ish but not actually well sounds hard. I would expect all but the hardest of hearts to be reluctant to dismiss a lowish performer, preferring to hope that experience and mentoring will yield a turnaround. People have empathy, after all. (Well, except for the sociopaths...)
In fact, to actually get managers to get rid of the merely adequate, you'd probably have to institute something like an up-or-out system, so managers could blame the system rather than themselves or the workers when the merely adequate got shoved out the door.