Actually, that's one thing I do know about Windows UI design. Some things that can work on both full windows and MDI windows use the same keystroke except with Alt for full windows and Ctrl for MDI windows. You'll find a lot of things that use Ctrl-F4. Most of them probably also use Ctrl-W, but I think that's a more recent one popularized by Netscape, honestly.

Also, feel free to blame the designers of the IBM PC-AT for putting your Control key in an awkward location.