got curious reading this thread. my kitchenaid mixer paddle aka beater appears to be powder coated as opposed to painted.
powder coating is a process where the metal part (beater) is electrostatically charged and fine powder - with an opposite electrical charge - is sprayed on. powder sticks, part goes through an oven, plastic powder melts onto the part creating a continuous coating.
many things can go wrong in that process - but as you've apparently bought multiple beaters/paddles which have failed in a similar fashion, it seems unlikely to be a "bad" batch from the powder coater. more suspect is that the manufacturer (ie Kitchenaid) may have changed their specifications. the sub-supplier (ie the powder coating place) is doing their job to spec, but the spec is not adequate. my KA is about 8 years old, the paddle has multiple dings where it's been rapped against the bowl, but it is not chipping or peeling.
googling about, I find replacement beaters in the 10-20 usd range. some are specifically cited as "nylon coated." glitch: I am not a chemist, but the KA statement that the coating is a polyester does not agree with the generally accepted makeup of "nylon." your mileage may vary.
regardless, a couple of points:
it's not painted,
it is not an enamel coating,
it is not galvanized
if you go down to the local hardware store an buy a chunk of "mill finish" aluminum, it will rub off a gray / dirty / dingy residue.
there is a process called "anodizing" which provides aluminum with a hard surface & finish. the anodized finish does not so readily produce the grungy rub off.
I did find a couple of web sites that offer "burnished finish" replacement paddles / beaters - base metal not specified - note in your searching, check for "beater" vs. "paddle" - terminology varies, salt to taste.
here's one: KitchenAid Mixer Flat Beaters, Wire Whips, and Dough Hooks from MarBeck.com beater whip
see also Amazon