Because one occurs every day on average in America...

Well it could be that... maybe they take the average of the two.

So Octavia, not every philly raptor question has an answer. But you did pique my curiosity. Turns out there's no set number of deaths or weight to tip the scale. It's totally up to prezident man. If it's a "dignitary" of America (and once an Israeli) then it can be one persons demise. Flag lowering for "regular citizens" deaths didn't seem to happen until the fall of the NYC twin towers, when Prez W had it lowered for the fallen firefighters.

Aaaand there's the rub! That would just have no impact and would just be demoralizing.