And a quick Google search reveals that a 1979 dollar is worth more than 5 today. At that rate, if that's correct, the threshold should be $50,000, which sounds more reasonable. (But 'reasonable' is not always their strong suit.)
And interestly, they have set the FATCA figure at $50,000.
I haven't lived in the US since 1989, so I always think dollars are worth so much more than they are. I'm often astounded when people tell me the prices of things.
Edit: Sorry, I meant to write 1970.