This picture is worth a thousand words. Theoretical, newborn baby sized clothes are for babies weighing 5-8lbs. As you can see from the picture, Gerber and Carters have hugely different views of what the size should be/is. On the left is a Gerber Newborn size side-snap shirt, and on the right is Carters version of the same. That's a very noticeable differnce if you ask me.
My girls outgrew the Gerber in less than two weeks and the Carters took us to four weeks. Gerber gets a solid thumbs down from me for quality - -you get what you pay for.