"Very rare" is, at best, a huge exaggeration. I can't post numbers, obviously, but from what I can tell based on employee available tools it's at least 25% of corporate employees. It seems rarer than it is for two reasons:

1. The company has grown rapidly, so many/most people seem fairly new. That doesn't mean that people that have been here a long time are leaving (although some obviously are). 2. The tool available to employees shows tenure of all employees, including fulfillment center workers, which are much less likely to be long-term.