In my experience, it's not overtly enforced. At lower levels there's an expectation of growth, so not growing can be seen as triggering a "fails to meet expectations." If someone is underperforming managers start to try to help them out and guide them, but after a string of "fails to meet" evaluations the focus shifts to motivation and compatibility with the company.

Almost nothing is unceremonious around here. Even employees who are on their way out are placed on performance improvement plans to give them a change to turn themselves around. I've never seen anyone fired: the closest I've seen is people leaving of their own accord to save themselves the trouble of going through the process.