I mistakenly hooked off the "Send Crash Reports automatically" button once, and have never been able to turn it off since (there is no equivalent off button in Apple's Crash Reporter dialog. How cunning!). Now, I've finally discovered where Apple hid the magic setting that sends any and all crash reports to Apple. The toggle is located in Console.app, located in your Utilities folder. Open it, then choose Preferences from the Console menu, and uncheck the "Automatically send anonymous diagnostic and usage statistics to Apple" button.

Screenshot of Console's preferences. Interestingly, after unchecking the setting, the button is disabled, and it has been ever since.
No longer shall Apple be flooded with crash reports from my own apps!