https://www.quora.com/Could-the-RPG-...e-Challenger-2
OK, it is from another game, it's accuracy is questionable but still, you can see that even in an M1A2 there ARE places that even a T54 can penetrate frontally (the area below the gun and the commander's hatch). It is just that the chance of hitting these spots is really low (and remember that even in WinSP the chance of hitting a weakspot is already very low).
I agree about the HEAT round variation in penetration (and HESH has even more, it can effectively double its penetration occasionally), but tbh I would prefer if the variation was as little as the KE and the weakspot penetration to be increased.
Lastly, about the GW M1 you mentioned, I'm not that surprised actually. The M1 has quite strong front side turret armor and also decent front side hull armor; a hit in these areas at a significant angle from an early T72's gun has little chance of penetrating. There are even more bizarre things in history, like for example a M4 Sherman tank in Ardennes that was hit by the 128mm AP shell of a Jagdtiger and the shell bouncing off the rear turret armor, because it hit at an extremely oblique angle. That has happened in the game many times as well, hitting targets at extreme angles and not killing them because of that. That being said, the opposite should also happen from time to time, an armored vehicle getting killed by a gun that on paper shouldn't penetrate because it hit a place where the armor is not as strong (and most modern tanks are full of places like that). Currently, unless you fight mostly early WW2 battles, you rarely see a weakspot hit translating to a penetration that normally shouldn't happen.
BTW, another good article about the armor layout of the initial M1. Here you can see that the turret side armor, as well as front side hull armor are quite different from the rest of the side armor of the tank:
https://below-the-turret-ring.blogsp...ite-armor.html