I used to make fun of Microsoft for their updates to non-essential software that, after installation, required a reboot. Apple has now trumped them. The recent update to Digital Camera Raw Compatibility "extends RAW file compatibility for Aperture 2 and iPhoto ’08 for the following cameras" and "also addresses issues related to specific cameras and overall stability". And it requires a reboot.
Note to Apple: this suggests that someone has messed up badly on determining which components of the operating system are critical to its operation.
Update:Post-Apple Chuqui explains it as a documentation error.