In statistics gadgets (Issue Statistics and Two Dimensional Filter Statistics), it will only show values if there are actually any issues associated with those values. It will not show possible values if there are zero issues associated. Let's say you have a field called 'Fruit' with 4 possible values : apple, banana, orange, grapes. Those gadgets will currently only show the first 3 rows below, not the last one. We need the last one to show , too. Same goes for columns, in a 2-dimensional gadget.
Please see http://jira.atlassian.com/browse/JRA-9626 which was originally opened for this request in JIRA portlets. That request was closed because you no longer have 'portlets' but now you have gadgets. To be honest, we could have just renamed that request.... Anyway, here is the new request.