The "Geiger Counter Numbers, How BAd is Bad?" article does not take into account that radiation sickness is a deterministic, or a non-stochastic health effect, which has a threshold. In other words the only way to get radiation sickness is to be exposed to high level radiation above the threshold over a short period of time. No amount of radiation below this threshold will cause the effect.
Stochastic health effects, most notably cancer, follow the LNT model, are random which may or may not be caused by radiation, and odds increase with increased exposer, but may not occur at all even at very high doses.
http://radiopaedia.org/articles/deterministic-effectsQuote:
Deterministic effects describe a cause and effect relationship between radiation and some side-effects. They are also called non-stochastic effects to contrast their relationship with the chance-like stochastic effects, e.g. of cancer induction.
Deterministic effects have a threshold below which, the effect does not occur. The threshold may be very small and may vary from person to person. However, once the threshold has been exceeded, the severity of an effect increases with dose.
Examples of deterministic effects (doses are given as absorbed dose):
skin erythema: 2-5Gy
irreversible skin damage: 20-40Gy
hair loss: 2-5Gy
sterility 2-3Gy
cataracts: 5Gy
lethality (whole body): 3-5Gy
fetal abnormality: 0.1-0.5Gy