Activity monitor can have more than one window, even though most people apparently never hit Cmd-1, Cmd-2, Cmd-3, or Cmd-4 to launch other windows. It also runs

Activity monitor can have more than one window, even though most people apparently never hit Cmd-1, Cmd-2, Cmd-3, or Cmd-4 to launch other windows. It also runs in live-icon mode with no windows at all. AFAIK, then, that leaves System Preferences as the sole exception to the normal model, and sure enough, that gets a lot of complaints from those of us who've been using Macs for long enough to remember when people at Apple really worked hard to implement the models consistently. There are some third-party apps that break the model, too, which is unfortunate.