That makes some sense, thanks. I was unaware of the chemistry involved, and that Rhodium would be preferable to Platinum if the two were priced equally. The other reason why a shift between metals would happen slowly is that the automakers have long term purchase agreements at pre-set price. PAL, for example, is currently selling Palladium to automakers at well above the current market price, which is a good thing for them, since their cost of production is also well above the current market price.
Carl