What does it matter if it is an extension of your keyboard? When you use these keypads, you use them in place of your keyboard. If you were to game with it, the only time you'd use your keyboard is when you type. The rest of the time you use the keypad instead. Otherwise, if you just want a few macro keys, you can get a gaming keyboard, or download AutoHotKey and macro on the keyboard itself.
You'll also notice in both the Nostromo and G13 cases, you'd move with your thumb d-pad or joystick. I've used both, and they make MMO gaming a much easier experience. You can move with your thumb, and use 4 fingers for hotkeys, move with 3 fingers, leaving you just your pinky and thumb to press hotkeys with...unless you let go of your movement keys.
I've used both. The Nostromo is more ergonomical, but the G13's Lua scripting abilities are superior.