I would point out that Windows programs written for different versions of the OS will appear different when running on the same machine. For instance, in my Windows 7 VM, LibreOffice has a white X on a red button to close the window, while Word has a black X on a grey background.
Hm, I haven't seen different versions of the close glyph, but I believe it. There are about 10 variations on contextual menus depending on what you're right clicking. I don't love that about Windows either.
As far as the general look and feel though, it still manages to feel more consistent. There are enough conventions like "clickable things have a hover effect" and relatively consistent styling of UI icons (pre-10 anyway) for it to feel like it's all one system.
