I see this fairly often on firmly-struck cross-side banks (exactly like Fatty's shot), but almost never on straight in shots. I'm not a physics guy, but if I had to take a stab at explaining why it happens on these shots, it would be this:
A banked ball has had more time/distance to acheive natural rolling, whereas a ball shot straight in, with speed, is likely to still be sliding when it gets to the hole. Natural rolling, at higher speeds, is going to produce the same effect as a pretty fair amount of follow, and, if you catch the point just right, it's enough spin to make the ball bend into the corner pocket. Another possible reason for this occuring more often on firmly-struck shots is that the firm speed compresses the point a little more, and this may make the angle of exit even more shallow in certain cirsumstances.
The last time this happened to me, the ob came off the rail at least a ball's width after hitting the point (I smacked it pretty good), and it still curved into the corner, so there's defnitely a spin-factor here.