It's not a bug. It's just the way SketchUp is designed to work. Personaly I've never found it a big problem or unproductive to enter radii instead of diameters. I'm fairly new to SketchUp though with only about 16 years under my belt. Pilou has provided some extensions that would help you out.
FWIW, since you are using SketchUp for your business, you need to be using SketchUp Pro, not SketchUp Make as you have listed in your profile.