Differential filter on input

[larrykvit]

I was looking at the schematic for this board and I saw a differential low pass filter on the inputs with resistor R3, R4, and capacitor C1.

From my calculation, the cut off frequency for this filter is f = 1/(2*pi * 2 * R * C) = 1/(2*pi * 2 * 100 * 0.1*10^-6) = 7957 hz

The sampling rate is 80 Hz on the ADC, so why is the cut off frequency so high? I would imagine you would want the cut off frequency to be less than nyquist so that you don't get any aliasing.