The resistance goes for electricity only afaik. I guess the whole idea in that theory is that the bottom part has more friction than the top part, thus turning the shell slightly more upwards on entering and on exiting, it's the top part that has more friction which then turns the shell more horizontal.
I don't think that's how it actually works though, considering how the shell gets deformed on impact and any change in direction would be very minimal. Also, all pictures I've seen of penetrations have straight holes.