There's a bit of selective editing going on here.
For example, the death toll from the Galveston, TX Hurricane of September 18, 1900 alone was about 8000, or the number of heat deaths cited in the article. The death toll of the San Francisco earthquake of 1906 was about 3400. Katrina's death toll was about 1800. There were other natural disasters further back in the 1800's that probably would have had a larger death toll if the area affected was as populated as it was today. See
http://genealogy.about.com/od/historic_disasters/tp/deadliest_us.htm and
https://en.wikipedia.org/wiki/List_of_United_States_disasters_by_death_toll .
The only really major earthquake the US in the last 100 years after San Francisco was the one in 1964 in sparsely populated Alaska (it had a death toll of 143). When the big one hits LA or San Francisco (again) the death toll could easily go into the thousands. Mount St. Helens erupted in a sparsely populated area, otherwise it could have killed thousands.
Heat waves are tricky. They affect mostly the elderly and infirm. We have a lot more people in this category today because of population growth and better health care. If you look at the list of natural disasters on the Wikipedia page I cited above, you'll see that bad heat waves generally cause deaths in the hundreds, not the thousands of other kinds of bad natural disasters. Heat waves do affect wider areas, and we get more of them than we do bad hurricanes and other natural disasters, so they add up. But let's not forget that the 8000 people killed by heat waves in the 25 years cited above is only 0.7% of the 1,096,372 US motor vehicle deaths in the same period (see
https://en.wikipedia.org/wiki/List_of_motor_vehicle_deaths_in_U.S._by_year ).
Death tolls from hurricanes, tornadoes, and most other natural disasters are generally less today because we are better at predicting them (on the other hand, the dollar cost of damage caused by natural disasters has gone up because of population growth and the fact that you can't move buildings out of the way). Heat waves are different because they aren't considered major disasters. This leaves the elderly and infirm to fend for themselves. Often these people cannot or do not want go to buildings with A/C. Others in inner cities leave their windows closed because they fear break-ins.
This is not to say that we shouldn't do more to find and help these people during heat waves, or that their lives are somehow worth less than others. If anything, it says we need to pay more attention to this hidden problem.
