not true
The material the capacitor is made of has the biggest influence on the tolerance. How it's made is the next biggest influence.
It's pretty hard to make a really big, really accurate capacitor, so you don't find a 1.0000000 farad capacitor.
Most high accuracy capacitors are made for low voltage circuits, but at least in theory, you could make a high voltage high accuracy capacitor.
But a .01ufd at 50V isn't going to be inherently more accurate than a .01ufd 20V capacitor.