On seeing this question, a point that occurred to me is that on this site it sometimes takes a while (from memory up to a day or so) for off-topic questions to be closed. If such questions were closed more quickly, this might reduce the frequency of answers to off-topic questions. This led me to check how many participants are able to vote to close questions, and I am puzzled by what I found.
The Privileges page in the Help Centre says that it needs 500+ rep. This would include about 100 people. But when voting myself to close a question, I have noticed an indicator that seems to be counting the possible voters down from 25 (ie if one person has already voted it will show 24 votes remaining). Is there a reason for this apparent discrepancy, or is it an error?