William-Sonoma Guide to Good Cooking installer 4.6.1 (bundled with all iMac computers) installs QuickTime extensions only if there are older versions or no QuickTime extensions active at the time of installation.
The installer checks to see if QuickTime extensions are installed in your extensions folder, and if present, what version you have. It also checks to see if the extensions are active.
If QuickTime is not active or its version is prior to 2.1, version 2.1 is installed. If you leave the QuickTime versions that come with Mac OS 8.1 or 8.5 active at the time of installation, it does not install any QuickTime extensions.