Really? Gnome definitely didn't come up with them, and most WMs have virtual desktops, but if you just launch X11 without a WM I definitely don't see any virtual desktops unless I'm missing something.
I'm a little rusty on this stuff (haven't messed with it for ~5 years) but IIRC you have the ICCCM specification and some non-standard but well adopted extensions[1] that define how a window manager communicates with the X server, and in this specification you will find all the virtual desktop goodies that every X window manager implements (including metacity, beryl, kwin, twm, fvwm2, etc).
In short, as far as virtual desktops go, what GNOME (metacity/beryl) does is the exactly same thing every window manager has been doing for the past decade at least, and the concept of virtual desktops (non-ICCCM+ implementations) goes much further back than that.
