... Another thing to mention is that asphalt is actually softer than concrete, enough to actually make a difference. So if you are able to run on the road instead of the sidewalk without getting run over, that could even help a bit too...
I'm not sure that asphalt is 'softer' then concrete when only the weight/force of a runner is applied. I personally think that it is the 'rougher' surface of the asphalt that allow the shoes to absorb more energy and therefore reduce impact.
I think that with the tiny peaks, the shoe is only initially contacting a small portion of surface area and then contacting more area exponentially (as the peaks widen to their bases). I think that it is the 'flatness' of concrete that forces all of the impact to occur in less time that makes it so jarring. Of course, you could have really flat asphalt and/or really rough concrete, so it'd be hard to even get an apples-to-apples comparison. Again, just personal opinions, and I am not disagreeing with the overall statement. Any thoughts?