The screen size advertised by Apple measures the "full screen" area, the undisturbed 16:10 rectangle of pixels. I just took measures on both a 14 and a 16 inch Macbook Pro. The screen we get is indeed slighly larger.

If you want to avoid the extra space, it's as easy as using a 16:10 resolution size. The menubar will drop down to the 16:10 space.