The Boston Marathon article, NEJM 4/14/2005 - fluid consumed (sports drink versus plain water) did not affect rates of hyponatremia.
2001 Capetown IM (a Noakes article), British Journal of Sports Medicine, 2006 - A randomized controlled trial. Athletes were given salt tablets or placebo tablets, and had no difference in sodium concentrations after the race. On average, athlete's took 15 salt tablets during the race, or the equivalent salt content to 9 liters of gatorade.
2. Heat Stroke.
IM Western Australia, British Journal of Sports Medicine, 2006 - 10 competitors swallowed temperature sensing "pills". Core temps increased 1 degree C, in spite of weight loss averaging 2.3kg, or 3%.
2000/2001 Cape Town IM (Noakes again), British Journal of Sports Medicine, 2004 - rectal temps of 700+ athletes. Weight gain or loss (as a surrogate for fluid intake) made no difference in rectal temps. As a group, people who lost 6% of their weight had no difference in rectal temp compared to those who lost only 2%. 6% is 10 pounds for me! More weight loss also trended towards faster times (so it's not as if they were working less and generating less heat).
As far as people (the media, race directors) being nervous nellies, people who die while racing either drop dead from coronary events, get caught in an accident, or drink themselves to death through hyponatremia. You can't prevent coronaries and accidents happen, but hyponatremia is preventable. Dehydration never killed anyone in a race. If you get dehydrated, you bonk, you sit down, rest, drink some water, and start again at a slower pace. If you get hyponatremic, you drink some water, feel worse, drink some more, get confused, your friends have you drink some more, then you seize and die. That's not to ignore that profound dehydration might affect performance, or that heat exhaustion happens; they're just not nearly as dangerous.