So °Brix from a refractometer is really a misnomer, at least not truly °Brix without dividing the reading by 1.04?

Not exactly. A degree Brix (or Plato) is equivalent to 1% of the solution (by weight) being sucrose. So if you have 1 kg of a 15°Bx sucrose solution, you have 150 g of sucrose and 850 g of water.

A refractometer doesn't measure the density of the solution, though. It measures the refractive index. Since the RI changes with changing sucrose concentration, you can calibrate a refractometer such that it will give a reading in °Bx instead of RI, saving you some time and effort in converting. Which is all well and good if you're making wine, since the sugars in grape must are almost entirely sucrose.

Beer wort is a mixture of a dozen or so sugars, and sucrose isn't even the most common (maltose is). So to use a refractometer to measure the density of wort, you have to use a different conversion from RI to density.

I see notations of RI_{i}^{1}, RI_{i}^{2}, RI_{i}^{3} ... But what is the numeric value in that?

The superscript is simply the exponential notation. x

^{2} is "x to the second power", x

^{3} is "x to the third power", etc.

The other item I didn't quite follow in your larger formula is where it says 0.0216*LN.

"ln" is the natural logarithm, a logarithm with e as the base. (e is a non-rational number equal to about 2.718.)

http://en.wikipedia.org/wiki/Natural_logarithmTruly, the ridiculously lengthy formula is just there for comic effect. If you actually want to convert refractometer readings either download the spreadsheet or use the online calculator.