Regarding cultural evolution. There seems to be a historical trend of accelerating evolution. Projected 10s of thousands of years back in time, this means that 1,000 years of technological evolution produced very little change. Prehistoric artifacts that survive are a small fraction of those made but those we have lots of (mainly stone tools) do follow an accelerating evolution path. Going back to cro magnum and older subspecies, we find 100,000s of years where technology remains unchanged. Big stone axes manufactured in the same places with the same methods. The Oldowan industry of ancient hominins existed, often using the same quarries for hundreds of thousands of years.
Also, we have cave painting sites in Australia with thousands of years of artwork where the tradition of cave painting survived into modern times. Some ancient sites even recorded the arrival for colonialists.
Ancient human history is strange. I agree on every point but… I think it's also good to keep an open mind and not allow our modern ideas of how human societies change, especially the pace of change colour our conclusions too much.
At the very least, It would seem to me that writing up a paragraph in the article to describe how the artwork evolved (or did not) over 14,000 years of human history would have added some insight.
I also find it highly suspect that they were comfortable going to three significant digits of accuracy in their dating, mentioning specific ages like "39,900 and 35,400" years old. Perhaps I've been away from science for too long, but when there is some probable chance of error, isn't it traditional to keep to the significant figures you are confident of (e.g. In this case - 40,000 years, 35,000 years)?
On the flip side - appeal to authority - this was a published paper in Nature - http://www.nature.com/nature/journal/v514/n7521/full/nature1..., so I presume those who know more than me thought otherwise.
I do find it really cool to discover that hand stencils show up all around the world in cave art though.