To contribute more physics to the dings argument
, dings and scratches reduce friction. Read on, but be warned, nerd material ahead.
There are two types of flow- laminar and turbulent. They are what they sound like. Laminar flow is when all the particles travel in a straight line parallel to each other, and slight distubances are neutralized because the particles form a sort of track for each other to put them back in line. Because the particles are all moving together, this type of flow creates the least friction against a surface, because the particles are not bouncing around. Turbulent flow is the opposite. If too great a disturbance is introduced into laminar flow, the particles start bouncing off of each other and a chain reaction begins, quickly causing the flow to become chaotic and turbulent. It is much easier to make this transition than to transition back to laminar flow. Because turbulent flow is bouncing all over the place, it pushes harder against a surface, creating more drag.
At this point, you may be wondering why the dings reduce friction, if they create turbulence, which increases drag. The answer is that it is more complicated than just laminar and turbulent flow. When a fluid passes over a surface, there is something known as a boundary layer. This is the layer of (in our case) air that is caught up in the friction of the disc, and not quite moving with the surrounding air. At the very surface of the disc, there is a layer of air that moves with the disc. As you progress outwards, the difference between the speed of the disc and the air increases, until the point at which the air is no longer moving with the disc at all. This is where the boundary layer ends.
A laminar boundary layer is thinner (and thus lighter in weight and more aerodynamic) than a turbulent boundary layer. However, there is a phenomenon called boundary layer seperation that occurs on bodies with very low Reynold's Numbers (read: less than a few feet from leading to trailing edge depending on the shape) In which this slowed down air actually seperates from the body, creating a tremendous amount of drag. Because of the chaotic movement of the particles, a turbulent boundary layer is much less likely to seperate than a laminar one, greatly out-weighing the additional drag is causes.
And now to how this effects stability.
As we know there are two components that reflect the stability of a disc, turn (the aerodynamic component) and fade (the gyroscopic component). dings affect both of these. As well as what i stated above, any ding, especially in the rim (where most of them happen), reduces the gyroscopic effect to some degree becuase of the removal of some of the spinning weight that causes it.
However, turn works differently. Turn is caused because of a lift imbalance stemming from the spin of a disc. For a RHBH row, the disc is spinning clockwise. This means that, relative to the air it is moving through, the left side of the disc is moving faster than the right. Because faster movement (usually) results in more lift the left side of the rises faster (or falls slower) than the right side, causing the lift vector to contain an upward component and a rightward component- this rightward component is the turn.
So why don't discs just always turn and burn? Because of the gyroscopic effect! Because I have never taken a physics class with any of this type of stuff (surprising huh?) I admit that I don't understand this part, other than that more spinning weight, especially farther out (like a lever) increases the force of the effect.
And I probably missed a few things, so be sure to ask about any holes in my description.
Edit: forgetting why the first part applies is kind of a biggie.
Basically, the decreased drag from the dings increases the amount of time in which turn overpowers fade, so it has time to turn farther before it slows down.
And credit for all this fluid dynamics knowledge goes to a book called Model Aircraft Aerodynamics, essentially discussing the aerodynamics of RC planes. The sizes are similar, meaning that many things apply to both, though the spin thing is exclusive to the discs.
/nerd rant
Also, I agree that PLH probably is probably the major factor, but there is at least some truth to the dings theory.
Edit: Didn't realze how long it was. Scary, I know, but if you want, you can skip over all the stuff in the middle.