I think of Windows (practically any flavor of it) as an "Operating Environment"; rather than a traditional "Operating System".
The purpose of an Operating System, in my belief of commonly-held theory, is that it is the basic services that interact with the hardware and allow software (applications, be it from the manufacuter or third-party) to run on a computer. Is this correct?
Talking about Windows (lets take XP for example): the OS allows one to write to a hard or floppy disk, manipulate files, or various aspects of displaying things. Windows as an OS, is lacking in support for CD-RW standards; we should fault Microsoft for not providing inherent services for using the CD-RW as common as using a Hard Disk or Floppy Disk. Windows as an OS really has no need for including such things like Instant Messaging, which is a software application--thus creating an Operating Environment.
It can be argued that an OS's job is to display and execute files. Going with this assumption, perhaps an OS of today has the responsibility of providing playback of MP3 or music files or displaying images. I can possibly go along with this.
But in the case of Linux, we all just know that all this GUI and X stuff is above and beyond the traditional OS. The kernel, if I'm not mistaken, is the actual OS; the little extra programs and GUI stuff creates the operating environment of a Mandrake, or Red Hat, etc.
Hence: DOS or the text-based Linux kernel is as core OS as one can get. Windows 3.1 brought about the operating environment which continues right through to XP. The typical Linux distributions we purchase/acquire today is equivalent to a GUI on top of DOS (just as Windows 3.1 started). Purchasing basic operating services has practically gone the way of the dinosaurs; would you go purchase DOS (version whatever) today?
Is this a true, clear picture of what a traditional OS is, and what we have come to expect in our purchases is actually an Operating Environment???
Tim
And yes for those wondering, I confirm that I do not condone alot of the current Microsoft practices. However my contribution to the topic and related discussion is meant to be clear and objective.