Name for the phenomenon where only the top few priority levels are used

Some folks, at least in the software engineering field, have called this tendency "Priority Inflation":

An instance of this problem is observed in the bug reporting process, where testers are encouraged to increase the reported priority in order to maximize the number of fixes delivered. This situation — called Priority Inflation by practitioners — is analyzed using game theory.
- "The Priority Inflation Game", Software Systems Engineering Group, UCL Department of Computer Science, University College London (paper in progress).

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The phenomenon I call priority inflation.... Over the past few years, I've seen a shift in the labelling of priorities in planning documents. A new priority has been introduced: Priority Zero. Nobody has explained to me what Priority 0 means, but I assume somebody invented it to emphasize that the feature is even more critical than priority 1. Mind you, I'm not sure what could be more important to a project than "If we don't do this, we're all fired." Maybe "If we don't do this, the earth will explode."
- "The great thing about priorities is that you can always go one higher", Raymond Chen, Microsoft, November 21, 2008.