Hi Caswell,
In addition to Edwin's suggestion it may help if you use a Custom List and select Test Case for the Type, after that add the Work Product column. This should display a list of your Test Cases with the Work Product column displaying the Defect or User Story that the case is associated to. You can then use the Advanced Filter to filter out the test cases that are not associated to items so only cases that belong to defect or stories are displayed, or you can leave it as is. When you have the columns you want you can do the export as before.
After reviewing Edwin's suggestion and your results it sounds like the query (Requirement != "null") is filtering some of the defects out because only the defects that have requirements are going to be displayed, which means that if the defect is not associated to a story it will not be displayed. If you remove the query do you get the full list of defects?
I hope that this information helps. Please let us know your questions.