I agree with schuon.
Excel anodize their rims. If powdercoating was better, I'm sure they would do it. But they don't.
Powdercoating is tough as nails. Ever wonder why John deer tractor parts are powder coated? Because it is durable, and still looks good. Powder coating is too labor intensive for excel to do it. They pump out tons of rims each day, and powder coating takes time to cure, and would be hard for a machine to evenly coat parts with. Anodizing is just letting them hang in a vat of acid for a few hours, and then pull them out. Powdercoating also adds mass.