To be sure, those interchanges are the most pleasant to drive through, but at a cost of land. The interchange design presented in the NPR article is much more feasible in urban centers where you might be constrained by existing structures. The accel/decel ramps can run parallel to the freeway, leading to nearly-right angle turns at street level. (It's not drawn this way in the article, but it doesn't take much imagination to picture it.)
That's definitely a good point, but in this particular case the picture posted elsewhere in the comments by raquo [1] looks like it could fit or almost-fit a parclo (possibly in a slightly elongated/compressed arrangement). The more hippie side of me is tempted to suggest that if you can't afford the land, you shouldn't be building an expressway there :)
Ditto on space constraints. Note also that in urban centers existing structures also include underground electricity, water supply, gas, phone lines, etc. which are usually very costly to relocate.
