Proposed new light-truck mileage regs.

From Forbes:

The proposed regulations would portion "light trucks" into six categories based on the square footage of the vehicle, or its so-called footprint. Smaller vehicles will have to meet more stringent fuel economy targets than bigger vehicles, and all would have to improve somewhat. By 2011, the last year the regulations cover, the smallest light trucks will be required to average 28.4 miles per gallon, and the biggest must average 21.3.

Question: don't the more stringent requirements for small trucks disincentivise manufacturers from building them? Why build a Ranger when it's both more profitable AND technologically easier to build an Excursion?

And if you're building a truck just smaller than the biggest category, but you can't get the mileage down to the category you're in, what's the logical decision? Make it bigger!