Why doesn't the "Ask Question" page give a short explanation when the "community wiki" checkbox should be checked?
Simply giving the checkbox a different caption might make it more obvious what CW is and when it should be selected, e.g:
[ ] make this a community wiki question if it is subjective or if there is no single correct answer
(of course this is just my interpretation of when the CW checkbox should be checked)
In any case, at least the FAQ should explain when the CW checkbox should be checked.