At poweron (iirc especially after an unclean power off) there is a chance that a current too high will flow through the LCD. I don't know if the fact that it happened once on a certain unit makes it more likely to happen again or, instead if it is completely random.
But it is _not_ related to wearing. It can happen on a brand new device as it can happen on a well seasoned one (I had it after 18 months). The only way to reduce the risk is to minimise the powercycles.