Are there any laptops that work this way? Why would anyone even want the lid open if they're not using the screen? A stand-alone keyboard is a lot more convenient and you can get one you like instead of the partial one most laptops have.
I repeat - are there any laptops that actually work this way? I have a pro and an air and as far as I know if the screen is open, it's turned on regardless of whether I have external monitors hooked up or not.
The original commenter was taking a dig at MacBooks, and I'm calling him on it - where does it say that the Pro will operate like this, and do any other laptops do it? Neither of mine seem to, and my work Dell doesn't either as far as I know.
If the lid is closed, you need to use an external keyboard (obviously). If the lid is open, you can choose to use either the built-in keyboard or an external one. No one ever said you couldn't use an external keyboard. The OP wants to use the built-in keyboard but not the built-in screen (i.e. the screen should be off). The commenter seems to think that it's an intentional anti-feature that is only available on the Pro model. I believe that there are no laptops that do this, and I wouldn't personally care to work that way even if they did.
So to answer your specific comment, the user is always free to use the built-in keyboard or an external keyboard. Unless, of course, the lid is closed - then you pretty much have to use an external keyboard.
I've always been able to disable the built-in display on all my XPS and Lenovo laptops. The choice was given to me to duplicate, extend or disable the built-in screen when casting or plugging external displays. It's also possible to disable the built-in display even if that's the only display available. It doesn't make sense in most cases but it is an option. (If you use your laptop as a cheap server for instance, you may want to keep it open due to how cooling works on XPS laptops)