In most cases a chip occurs on the wheel somewhere, either from a rock chip or from the owner, like when putting lugs back on or using a wrench near the lugs area. Sometimes when a shop mounts a tire to the wheel.
The wheels are highly polished beneath the clear coat which gives them a relatively smooth surface, not the kind that takes paint very well. Why do body shops scuff the car before the paint goes on? To give the surface a texture with which the paint can bite. Usually the factory will do a better job at clearing the wheels because they typically bake the part for a period of time.
Unfortunately, as soon as one small chip occurs, water, cleaning products, and/or other debris can work it's way underneath the paint lifting it up every time is is caught by something, like a towel for example.
I hate to say it but once it starts, there is pretty much nothing to stop it, and it usually gets worse. I had this problem on a set of HRE's, that started with a tire shop chipping the very edge while mounting a tire.
I know why the factory puts the clear on, so that people don't have to put so much elbow grease into keeping them shiny. But in all honesty I would have the clear removed, and have them polished. The maintenence is more, but if you scratch or nick the surface you can polish back out again, with the clear coat being so delicate, if this where to happen to it, you pretty much have to start over.
