... What you're referring to as Linux, is in fact, GNU/Linux, or as I've recently taken to calling it, GNU plus Linux. Linux is not an operating system unto itself, but rather another free component of a fully functioning GNU system made useful by the GNU corelibs, shell utilities and vital system components comprising a full OS as defined by POSIX.
Many computer users run a modified version of the GNU system every day, without realizing it. Through a peculiar turn of events, the version of GNU which is widely used today is often called "Linux", and many of its users are not aware that it is basically the GNU system, developed by the GNU Project.
There really is a Linux, and these people are using it, but it is just a part of the system they use. Linux is the kernel: the program in the system that allocates the machine's resources to the other programs that you run. The kernel is an essential part of an operating system, but useless by itself; it can only function in the context of a complete operating system. Linux is normally used in combination with the GNU operating system: the whole system is basically GNU with Linux added, or GNU/Linux. All the so-called "Linux" distributions are really distributions of GNU/Linux.
Alright Richard Stallman, why'd you have to kill Aniday and wear his online persona as a suit?
More seriously, I don't think it matters:
GNU isn't an OS*, it's a collection of programs (including shells to allow interaction with the kernel) that sit on top of the Linux kernel. Likewise, as you say, Linux isn't a full OS either. Each of them are modular halves of an OS.
Sure, in theory you could use other shells and such on top of the Linux kernel, or wrap GNU software around a different kernel, but since that's largely not done there's no confusion if you just say "Linux".
So the choice is between an unwieldy name that most people don't know and that adds nothing to the clarity of the speaker, or a simpler, already-accepted, one that's just as unambiguous. Me, I favour the latter.
*Well, technically it is, but it's such an early alpha, despite almost 30 years of development, that it really doesn't count.
I'd just like to interject for a moment: what you're referring to as Windows 8 is, in fact, Windows 7 /Metrosexual UI. Or, as I've taken to calling it: Windows 7 + Metrosexual UI.
Stallman tends to be very specific in his terming of things.
His speech has made itself into a meme of its own.
"Let us not seek the Republican answer or the Democratic answer,
but the right answer. Let us not seek to fix the blame for the past.
Let us accept our own responsibility for the future." - John F. Kennedy