It's called Apple Software UPDATE... not Apple Software ADDITION. The tool should be used as it was originally unveiled to the public, as a means of distributing important and often security-related updates to Apple software already installed on the user's computer. Using it to drive up the install base of other software products that users might not want or need is an inappropriate use of the tool. People saying it is within Apple's rights to quietly install new products on those machines just don't seem to understand the concept of only installing the software you need.
Yes, users should know better. They should read the dialog boxes. They should see there is an option to opt out. But often times they don't, and that's no excuse for Apple's attempt to exploit end-user ignorance and/or apathy.
Apple complained when Microsoft made a similar move with their Windows Update software. Now you'll notice that Microsoft Update will offer software not currently installed on a user's computer, but it won't be checked by default, meaning the user must make an active decision to install it if they so choose. Why can't Apple take the same approach?
It's called Apple Software