So, as it turns out, iPhoto does import images from Photo Stream automatically:
Keeping a complete set of your photos on your Mac is as simple as turning on Photo Stream in iPhoto or Aperture. Every new photo you take appears in a Photo Stream album just as it does on your iPhone, iPad, and iPod touch. But since your Mac has more storage than your iOS device, it automatically imports every picture from your Photo Stream into your photo library so you can edit, delete, and share the ones you want.
Thanks to everyone who emailed me about this. I try not to make such glaring errors in my writing — please consider this my apology.