Right on the money!!It's all dependent on how often you clean the balls, and how much polish is used...
Naturally, to think that the balls will spin on the same axis every time you run them is just unrealistic. That said, it could take years, for the effect to be noticeable.
Something to note: If the design has no implements which cause an axial shift during a cycle, the amount of wear along that axis will increase over time. Once the balls start to become ellipsoidal, they will have a natural tendency to consistently spin about the major axis, thereby accelerating the wear about the major axis.
It may not be noticeable to the naked eye, though it could be measured, and would certainly be noticeable when racking the balls. This would become most obvious in a poolhall setting, with frequent cleanings.