52x speed has been the limit for a long time because the outside edge of the CD gets to speeds where it could damage itself. I guess it would need a cushion, like a nearly applied (car/bike) disc brake.

You're forgetting the square-cube law. Or rather, in this case the linear-square law. Think of each bit as a square, with side length 1/n. Oversimplifying, but the basic principle is there.

The total amount of data the laser goes over in a second is proportional to n - because it's related to how long the laser takes to get from one edge of the square the the other edge. But the total amount of information stored goes up as n^2 - it's related to the area of the square.

Or: to put it another way, the number of tracks also goes up when data density increases.

(This also happens with hard drives over time. Recent hard drives take a lot longer to read or write the entire drive than older ones. See http://tylermuth.wordpress.com/2011/11/02/a-little-hard-driv... for example.)