"the reason for rattling off radio instructions at breakneck speed and non-standard radio calls if for traffic. When you have the congestion you have over here.."
At airports the likes of KLAX, I might agree, druglord, however my experience there was that there were often Say agains from foreign crewed aircraft that had arrived there tired after a longhaul flight, and whose first language is not English.
However, American controlllers also work in other countries eg. Japan, Guam, in control zones where traffic is NOT a factor, and on the whole their delivery is Gatling gun fast.
It's UNnecessary and counter-productive, imo.