The dark ages were not years with no progress.However, to see these people play it as not bad is a little crazy.  During the American depression there was advancements and progress but I don't here anybody saying it was happy times it was still named appropriately just like the Dark Ages.

The link doesn't seem to be working for the article.  It is a shame I would very much like to read it but I think there is a lot of factors attributing to farm life and longevity.  There are pesticides for sure but in the country they are also farther away from all the other pollutants that city life brings factories and car emissions.  Fast food is rampant in the cities and I think a farmer is more likely to eat more vegetables and such as they are growing them and staying away from the chemical processed foods.I'm sure that stress is a factor as you said but I bet there is a lot of diet based reasons too.  As you said manual labor you can find anywhere so I would rule that out.