Originally Posted by
dabac
1. Style. Aluminium is notoriously difficult to paint. Anodizing allows for a range of colours, w/o any weight penalty and with a more durable result.
2. Weather-proofing. Anodizing does render the rim more corrosion resistant. As a 4-season rider in a place where winter means salted roads, this means both better rim life and better aestethics.
3. (speculative) Brittle also means stiffer. And there is an advantage to stiff rims - assuming you get the properties right.
I'll add further that anodizing is only a surface treatment. The anodized layer is only a few microns thick. Additionally, aluminum is a reactive metal that forms a thin oxidized layer on the surface as soon as fresh aluminum is exposed to the oxygen in the air. Anodizing...oxidation of the surface layer by means of electron transfer...is only slightly thicker than air oxidation.