"Are there really millions of 6000lb SUVs on the road? Are there truly only a few thousand Porsches on the road?"
There have been about 350,000 Porsches produced worldwide. About half are in the U.S. Presumably more than half are on the road, but I'm not sure where I'd find out actual numbers.
Since 1989, 3.1 million SUVs have been sold, and God knows how many "Class 8" trucks which have a Federal tax incentive* that's being applied to the 6,000 lb SUVs as well.
I don't have a weight class breakout, but yes, it's totalling in the millions.
*
http://waw.wardsauto.com/ar/auto_loophole_big_enough/