Well, I just - in effect - paid $15 to upgrade Preview. I never use iPhoto, but I paid the $15 to upgrade from iPhoto '09 (8.xx) to iPhoto '11 (9.xx), and then installed Digital Camera Raw Compatibility Update 3.12. When I start iPhoto, it tells me that the photo library needs to be upgraded, and it will take a long time; since I don't use iPhoto, this is of no concern to me, so I press Quit.
And after all that, Preview finally supports 5D Mark III raw files. I have to wonder if Apple will ever get around to adding a Preview upgrade that would make this iPhoto/Aperture upgrade unnecessary. I just got tired of waiting.
After waiting for a non-Beta version of Lightroom or Adobe Camera Raw and waiting for a defined solution to the light leak problem, I decided to work around the one minor but annoying issue which I could do something about. Humph!!!