Certainly a valid point. However, from my own experience (yours may certainly vary), tire traction in the wet is not that much less than when dry, so the limiting factor that I've run into with rim brakes is a dramatic reduction in effectiveness when compared to my BB7's (I use 185mm G3 and XTR ICE rotors, for context). This is particularly noticeable with a loaded commuter - the bike alone is ~35 pounds with fenders, racks and such, plus another 15-20 in the panniers depending on the day. Since I know you're a sciencey type of a guy, you'll know that the added weight actually contributes to the friction/traction while simultaneously adding to the momentum. I know that speed contributes far more to the whole momentum thing, but my point is that I've found rim brakes to be the weak point in the wet, not traction.

In the snow/ice, I ride studded tires, which does help, though the differential is not as great assuming it is a dry cold. In those conditions, modulation is my best friend.

For mountain biking, I'd tend to agree with you (again from my own experience with my SD-7 V- brakes) because when conditions are wet, the added wet braking effectiveness of discs is pointless if the trail is slick.