I would think the automobile is the primary factor in why it isn't lower. (Looking at wikipedia, traffic accidents account for 2.09% of deaths, the next accident category, falls, is 0.69% http://en.wikipedia.org/wiki/List_of_causes_of_death_by_rate )

I was actually surprised at how little it has changed relative to the amount of safety regulations and technology. I always pictured the years around 1900 as being much more physically dangerous.

And different jobs - a printer jam doesn't do quite the same damage as an explosion in a coal mine.

Accident RATES in factories have gone down a lot, construction/farming a little less so - but the number of peopel exposed to the risk environment has dropped a lot