Lava kills that many people? I did die in it a couple times while mining obsidian, but at the same time learned from that experience how to work in areas with lava above, adjacent to, and below me without putting myself or the ores I was acquiring in danger. I also learned to always carry a water bucket. I tend to react quickly enough when I laterally mine into a hidden pocket that I get away and block the leak with no trouble, and I only break the "don't dig straight down" rule when I know what's below me (well, okay, sometimes I will when it's just one block and I'm feeling really lazy).
Carving cliffs and building towers has, for some reason, not schooled me so well in safety practices, possibly because death by gravity is not nearly as inconvenient as death by lava. I built a miniature Final Fantasy IV Tower of Bab-il that went from the void to the clouds (in a world where bedrock is replaced by lava), and hollowed out the ground surrounding it. Died like 5 times building the thing and carving away the cliffs.