At least for Mac part, the OS comes as a package. There is a special program "Pacifist" that can open the package and there you will see "other OS files". Don't know how does it look like under Windows. Guess, the installer disk was not meant to mount under that OS.
This is a "how do they do that" question. I recently got a new printer. I use an IMac with "Snow Leopard" and Parallels running Win XP. Never mind why the Parallels but just focus on the 2 operating systems. When I place the installation disk in under Snow Leopard, I see in the finder an installation program and a Manuals folder with installation and usage information. When I insert the installation disk under Windows, I see setup files, a whole bunch of program files, and a Manuals folder. With either OS, I don't see the other OS's files. How do they do that?