I've only recently understood what the percentage figures on the All Privileges page mean and was confused about them until now. This aspect could use further clarification on that page.
I used to think it reflected what percentage of the total user base had each given privilege, either currently or as a hard limit (i.e. a fixed percentage always had a specific privilege and the points required changed over time). The latter obviously makes a lot less sense than the former. Now I finally understand what it actually means: You personally are this far towards having this privilege yourself.
Perhaps the phrase 'completion percentage' can be used at the bottom of the sidebar on that page? Especially with the broadening scope of the Stack Exchange network, this aspect should be explained a little more obviously.