In layman's terms, as you put it, refraction of light is the change in direction of light. In this purpose, it's different than reflection. Reflection is the change of light solely on the surface of the material in question. Refraction, when in the consideration of fluorocarbon line is how light changes direction on not only the surface of the line, but as lightwaves travel through the material. In this case, light is bent at different lengths, better to camoflauge the surface of the line, in this case it's nearly cylindrical. Think of it like this, reflection is going to act like a mirror, refraction is going to act as a lens. In the case of fluorocarbon, that lens surface is very similar to that of the water surrounding it, therefore it has a lower profile. Nylon reflects almost the entire visible spectrum. Fluoro bends light as it enters one side, and goes out at a different angle. Mono bends light as it reflect of the surface; primary difference. There's a large difference between the two.
In terms of the refractive index, most finished nylon mono is considerably higher than what you'd listed. In most cases, it's well above the 1.6 marker. The finished material in fluorocarbon, and yes, there's a difference in resins... is generally about 1.41 or 1.42. The secondary aspect to fluorocarbon's refractive index is that it's nearly impermeable to UV degradation, the same cannot be said of Mono.
If it doesn't make a difference, and it's entirely a gimmick, then I must be the luckiest guy ever. There are far to many demonstable instances in which I've been on clear water lakes and fished 15lb fluoro and the guy fishing 6lb mono was getting back-boated 9:1. Sure, there could have been other differences, like the fall rate and those sorts of things, however fishing a 3/16 ounce shakey head with the exact same worm, all fish were coming dead-sticked on bottom. It wasn't a matte rof fall rate, it wasn't a difference in baits, or technique. The sole difference was the line in question.