Voltage regulator's input capacitor "Required if regulator is locate an appreciable distance from power supply filter."
It depends on what the 78xx is powering. If you have a noisy load then the input cap obviously matters much more and I would provide one if the distance is more than an inch or two. Maybe provide a footprint and populate a cap if EMI testing shows that you need to (to constrain the loop area of high frequency currents). Use fat power traces to keep impedance low.

I wouldn't worry about 10mm from cap to 78xx at all.