Does any one know why laptop manufacturers swap the function keys (F1 - F12) on top with non-vital laptop keys?

I noticed it a while ago on my friend's new Dell laptop, and now on my wife's new Lenovo as well. It's rather annoying, when you try and close a program you can't just press Alt+F4, but rather FN+Alt+F4 - which doesn't always work that well either.

anyhow, I'm just curious as to why they did this......