the ford explorer has been the best selling suv for a long time. practically since it came out in 1991. this is due, in my opinion to the supply being there to support the demand. jeep has made suv's longer, but the cherokee was too small to satisfy a family of more than 4, and the grand cherokee didnt come out until late in 93. the explorer and the s-10 blazer were well entrenched by then. jeep has never rivalled ford's numbers. mainly, i think because of production amounts. also government fleet deals.
what i'm stumbling around saying is that you two (hm&ut) are both right. there has to be a demand, but if there is no supply, the demand is filled in other ways. if there were no SUV's you'd still see a lot of conversion vans.