If you don't buy it, I assume that you have solid alternate explanations of why the trends in vehicle size/power/design seem to closely track the preferences expressed by federal policy (intentionally or not) along with fuel costs.

Yes, there are (largely misguided but in some senses game-theory justified) preferences for higher/larger/heavier vehicles. But from what I've read, these don't provide much (statistical) explanatory power for the actual numbers.