So attaching the iPhone to a cable triggers camera behavior. If you don't like iPhoto or Aperture launching on connection, you have to override this behavior for all camera-like devices.
I sort of figured that out, but where do you change this? It's not in system preferences -- where it should be.
Turns out it's buried in Image Capture preferences (tsk, tsk Apple). I knew that once, but my brain has trouble remembering illogical things.
Thank you TUAW and Google:
Stop your iPhone from auto-launching iPhoto (or Aperture, etc.) - The Unofficial Apple Weblog (TUAW)
... One particularly annoying thing about plugging in my iPhone is that it always launches Aperture and prompts for permission to import photos. While you should be able to turn this off (in the preferences of the Image Capture application)...