Why are Taurine and Arginine essential components of the feline diet?
From the Taurine Wikipedia article:


  The absence of taurine causes a cat's retina to slowly degenerate, causing eye problems and (eventually) irreversible blindness – a condition known as central retinal degeneration (CRD), as well as hair loss and tooth decay. Decreased plasma taurine concentration has been demonstrated to be associated with feline dilated cardiomyopathy.


Arginine is an Essential Amino Acid for cats (and many other mammals - including Humans while we're infants). That is, they cannot synthesize it on their own and must obtain it entirely from their diet. A 10lb. (5kg) cat will require about .86g of Arginine - which is abundant in all meats and can be met with a few ounces of food.

I could not find anything particularly special about Arginine as opposed to other EAA's for cats.