A lot of it is the type of material you use in the construction of the ski. When you pop, you sorta ollie, like lean back and then spring off the tails. You can do this on flat skis, you can do it on rockered skis (though the contact point is moved closer to the center of the ski).
I find that what determines the spring and pop of skis is part camber, but a surprising amount is determined by what type of materials are in the ski. Different types of cores want to spring back to their natural configuration at different rates. Different ways of using fiberglass in construction can vastly change the feel of a ski as well. Metals and carbon fiber have effects too when pressed into a ski, and even small changes in the length and location of these in a ski can make big changes in a completed ski.
Dont be skeptical. Well, maybe be skeptical. Its taken the industry a few years to figure out how to get the best pop out of skis with these new camber profiles, but the current generation of rockered park skis are pretty amazing.