Based on the discussion about The Stack Overflow Question Lifecycle, which I'd characterize very broadly this way...
Programming Related Question -> Answers! Non-Programming Related Question -> Closed -> Deleted (eventually, depending)
... I thought it would be a good idea to couch the discussion in terms of actual data. Here's a breakdown of all the Stack Overflow questions and answers to date:
Closed DeletedQuestions 150,433 5,900 9,794Answers 625,734 n/a 55,765
The number of closed questions is not quite 4% of all questions ever asked.
Remember that we do not require any form of registration; we allow totally anonymous users to ask whatever they want. Even a hard-line inclusionist would agree that half of those closed questions should have been closed as obviously not programming related, spam, or garbage. (Also, if you are a dogmatist who thinks no Stack Overflow question should ever be closed for any reason, Stack Overflow is probably not the right website for you.)
So that means when we cast close and open votes on a question, we are disagreeing about one question in every fifty.