I don't think it's chemistry so much as simply knowing what the hell things are made of.

I had presumed that, apart from the ability to use one centre with a number of rim widths (and one set of rims for a number of centre styles), the other reason was so that a nice shiny and tough spun (stainless) steel rim could be used, but I imagine weight might be a good reason not to do so. Anyway, sorry to drag this off topic...
Edit: Chem was my best subject in yr12.