Blender's measurement system is little broken. Probably that is not ever even noticed, but when you create a cube (or any object), it is not what you expect it to be. The correct size of the new created objects is always inputted size / 2.
Oh, you are very much right, sorry about this confusion.
But would it be better to use diameters when creating new object instead of radius? For example if I'm box modeling house that is 15m x 8m x 5m. Now I need to create box and type 7.5m, to get that 15m. Then when the box is made, I need to scale the Y dimension to 8m and Z to 5m and then apply scale.
If I could type those dimensions to the new cube right at the beginning and maybe even add some subdivisions, it would make starting little bit faster.