It’s funny, a friend of mine and I were talking about the same thing yesterday. A couple of posters here have pointed out that Newton needed a transition shoe for people who were not ‘natural runners’ who needed some ability to mix in heel-striking running with the mid-foot strike as they adapt their stride. You can do a lot of calf exercises to strengthen the muscles for both flexion and extension as part of your adaptation process or before you try to switch, but this does not typically happen and when a runner gets tired and their calves get cooked from the mid-foot running style that their body is not used to one of two things happen - they get tendonitis in their lower legs or they switch to heel-striking in a shoe that is specifically not designed for it and end up with impact injuries. Either way it is not a great way to sell your shoes. The heel-striking option eases transition without selling out the concept behind the shoes.
Of course the same shoe also opens up a huge market for people who want Newton Shoes but don’t want to mid/fore-foot strike. That way everyone that wants to be like Crowie or their other favorite Newton Runner, but doesn’t have the mechanics to use their shoes can buy Newton and still run the way they want. This is something of an unstated benefit of those shoes. The third benefit is that if you get people who are curious about the shoes to try the heel-strike shoes (assuming they are not ‘natural runners’) and the like the fit, construction, and the action/reaction technology, they may open up to the wisdom behind the natural running technique and switch over to Newton full-stop.
Finally, I was playing with the Distance and Distance S the other day when grabbing a friend for lunch at Newton and there is a specific firmer area of midsole under the arch of the S. The Distance has what feels like the same durometer of material on the lateral and corresponding medial side of the shoe, while the S has firmer material in front of the heel on the medial side compared to the lateral. Logically this would suggest better support under the mid-foot and arch as the mid-foot runner strikes if their foot is pronated at impact (different from a foot pronating through the stride, which, as has been pointed out, is natural).
I live in Boulder and know a few people at Newton. I have to say they are some really great folks and have a dedication to the concept, the brand, and truly making people’s running experience better. Whether you like the shoes or not, there is no question that it is a quality company that is selling something ‘real’ rather than simply a gimmick or ‘me-too-cool.’