Death World/Headscratchers

"The difference is that fictional Deathworlds are more interesting. Generally this means they have a relatively breathable atmosphere, have a compelling reason for characters to get out and walk around, and have a variety of dangerous flora and fauna to menace them."
 * How is it that on a great many planets that are classified as Death Worlds, the characters can breathe the air with no problem? Wouldn't only a planet that's totally inimical to human life, like say Venus, really be a Death World by our standards?
 * If the air isn't breathable, then it's not really a Death World. Per trope description:


 * Ah, okay. The amazing things one can learn by reading >_<