I have yet to see actual scientific evidence that a human can tell the difference between asphalt and concrete. The anecdotes are all from runners. Not really unbiased. If I saw machine-measured shock data simulating a running 100+ pound human being, I'd be more inclined to believe it, so I'm open-minded but skeptical.

Somebody call Mythbusters!

My own theory is that what's really going on is sidewalks aren't nearly as level as a street, with the slabs of concrete pitching in various subtle directions and having uneven joints. That will affect a runner in a negative way.

As for joggers in the bike lane, if it's actually "bikes only", then the peds shouldn't be there.