This passage from a reader email pretty much nails it:

Yes, it would make a difference if the checkbox for Safari were unchecked by default. Also, the “new installs” should be visually separated from the “updates to programs you’ve already installed”, and clearly marked as such. I’m all in favor of programs updating themselves — especially potentially network-exploitable apps like iTunes or QuickTime — but companies shouldn’t abuse that to push entirely unrelated software on end users.

The reason reactions to this controversy have been so polarized is that we’ve been mostly arguing about the wrong thing: how or whether Apple should offer new applications to Windows users via the current Software Update app. The problem is with the design of the Software Update app itself.

The reader is right: updates to currently-installed software are an entirely different thing than offers to install new software. Different things should look different; the current design of Software Update doesn’t allow for such a visual differentiation.

For updates to installed software, the simple plain list Software Update currently displays is perfect. New software — like, in this case, Safari — should be displayed separately and more prominently. A big app icon alongside a brief description, perhaps — something that, visually, is instantly recognizable as something different from the regular updates. It should be clear that what’s being offered is both new and optional. The default should be not to install — or, perhaps, the user could be required to explicitly click either “Install” or “Don’t Install”, with neither option selected by default. If the user chooses “Don’t Install”, Software Update should then offer the user the option to never again be prompted about this particular application. (You can do this now, using the “Ignore Update” command in the Update menu, but this feature should not be hidden in a menu.)

Maybe Apple realizes this, but they figured it wasn’t worth the effort to add an entirely new presentation mode to the Software Update app, because they don’t have any other new Windows apps on the horizon. I.e., that, given their current plans, it wouldn’t be a new “ask the user if they want this brand new app installed” feature, but rather, for all intents and purposes, really just an “ask the user if they want Safari” feature.

But laziness is no excuse. This entire controversy, minuscule though it may be, could — and should — have been avoided if Apple had followed the design principle of making things that are different look different.