...but, rather, it is an undisputable fact that a cleaned chip in identical condition to another that has not been cleaned will sell for a higher price 100% of the time. I've seen this pattern for more than 10 years now, especially on eBay, and I know that one highly respected high-volume chip dealer cleans virtually every chip he sells just for this reason.
Maybe one of the reasons that cleaning is so prevalent in this hobby and not in some others is that an uncleaned chip is most likely germ-ridden and can possibly carry disease. I heard on the radio earlier this week a list of the most unsanitary jobs, and the top ones were those where people handled money. I would bet that a hard-surfaced casino chip with little nooks and crannies is much better able to collect and carry germs than is paper money. Take a good long look at Mark's top scan. What do you suppose that dirt is comprised of? History is one thing, but the threat of disease seems to offset that.