I think you confuse the term scale with dimension. Changing the scale is always a percentage value of the object's size. If your cube is 2 [whateverunit] and you type "S - 1.1" it now has 2 [whateverunit] multiplied by 1.1
The only method of changing an object's size directly without using percentages I know of is manipulating its dimensions which you can find directly below the scale settings in the properties shelf. AFAIK there are no keyboard shortcuts to manipulate the dimension values directly - maybe due to the fact that Blender never intended to be an accurate CAD like software.