Why can't I delete certain content types? I have a Drupal 7 site, and under the Content Types menu, only certain types have a 'delete' link under the 'Operations' column. 

All of the content types have the links for 'edit', 'manage fields', and 'manage display', but only some have 'delete', while others don't. 

I checked my permissions for my user, and I do have Administer content types -- but that appears to be one global permission for all content types, so I still don't understand why some are deletable while others aren't. 

Why do only certain content types have a delete operation?
Delete them by going to the url /admin/structure/types/manage/content-machine-name/delete

content-machine-name being the machine name of the content type you want to delete. Also, make sure you use dashes in the machine name rather then underscores.