I can't comment because my reputation doesn't carry over. To the ones that said scale adjusts the dims, sure. okay - you're missing the point.
To the guy that said it's because there's inherent beauty in causing people to get mad, go insane trying to figure out idiotic scales to model a real world object... I just want to ask you this. Model a simple, hand built set of steps some time using real world dimensions, and then in the middle of your frustration, remember that you said that it was beautiful and you can't see any difference. Also, note that transferring the object to any other program, such as Unity, or 3d printer, completely destroys the dimensions.
And to the person that pointed out the "one more reason: all vertices..." base vertices would be expressed in floating point numbers, so, your example should be stated as -1 to 1... meaning that 0.5 would be a very easy, and a nice, neat number to have. but 100% props for thinking, and not missing the point.
The simplest answer is that the programmers chose radius instead of logical dimensions because they were drop on their heads as children and fed a diet of lead paint chips. And, it's this reason that blender is not accepted at any of the companies that I have ever applied for, worked for, or managed. Including my own company.
To be honest, I have never seen a cube expressed in radius as it's primary measurement.
In my mind, I would say that the better question to ask is ... how do we just fix the underlying object so that we can move on with life? I ask this because for me, sadly, Maya is currently not an option... though I would make religious sacrifices to the dark gods if they made it an option.