I have worked at a few firms that have done this, and I have heard from a few people their managers arbitrarily picked them to get knocked into a lower tier.
Conversely, if they hired a big cohort of bozos one year, you know they would never say, "We would like to get rid of 15%, but our plan is only to get rid of 10%." They would have no problem going beyond 10%.
It is if made overnight!
And clarify the difference between skilled and unskilled labor (which might make this make more sense), this is not a description of the work itself, but rather the barrier of entry. Anyone can be taken off the street and trained into an "unskilled" position with relative ease. That is not true for "skilled" positions though. Which is why Amazon's decision to start cutting corporate jobs represents a fundamental shift in their path going forward.